Recently when I attempted to connect an external USB hard drive to the computer a message appeared saying “USB device not recognised” with the additional explanation that the device has malfunctioned. The same message appeared when I tried connecting a variety of different USB flash drives. The upshot is that I cannot access the drives on the computer. Each of the drives was tested on a different computer and they work fine, so the problem seems to be my computer. It certainly creates a lack of confidence if important data is stored on external hard drives to which access can be refused so randomly. The computer is running Windows XP.

It is quite frustrating when such errors occur at random times, especially if important data is contained on the drive which has lost access. However, as you have tested the drives on a different computer and they work correctly at least the data itself is safe, which means that the problem lies with your computer not recognising and reading the USB drives correctly. There are several possible reasons that this problem could be occurring, so we will work through the various possibilities sequentially hopefully finding one which resolves the problem.

The first suggestion which is always floated when experiencing USB-related problems is to ensure that you are connecting the devices directly to the USB port on the computer and are not going through a USB hub. Occasionally USB hubs can cause problems, particularly un-powered hubs, as too many devices may be connected to the hub and the power output from the connected USB port is not sufficient to power all the connected devices. In any case, make sure that you are connecting the devices directly to the computer’s USB port. If you were using a USB hub and now find when connecting the device directly to the USB port that the problem no longer occurs, the issue is related to the USB hub. In this instance, either do not connect that device through a USB hub to the computer or the hub itself may be faulty and you should consider purchasing a new USB hub.

Assuming that you are connecting the devices directly to a computer USB port, yet the problems continue, we need to check whether the problem is localised to a particular USB port(s) or affects all USB ports, as this will be indicative of whether the problem is a faulty USB port (or USB controller) versus a more general problem. Try plugging the device into a different USB port. For example, if you are currently plugging the device into one of the USB ports on the front of the computer then try plugging the device into a different USB port on the front of the computer. If you encounter the same problem then the issue is not a specific USB port. However, USB ports which are physically next to each other generally use the same USB controller (or root hub) on the motherboard inside the computer. Therefore, the problem could be with that USB controller and thus affecting both ports on the front of the computer. To eliminate this possibility, try plugging the device into a USB port on the back of the computer. Since these are in a completely different location it is likely they are using a different USB controller. Should you find that the problem no longer occurs, then it seems there is a hardware problem with one of the USB controllers on the motherboard. Likewise, if the problem only occurs on one USB port then the problem is likely hardware-related to do with that particular USB port. In this situation there is not much you can do, given the hardware-related nature of this problem. In this case, I suggest you take the computer into a computer repair shop to have the problem resolved. Unless there is an obvious problem with the motherboard USB configuration, I imagine that the motherboard itself will need to be replaced. Depending on which other components need to be replaced (as some components may be dependent on the particular type of motherboard installed) it could cost a few hundred dollars. However, this will be clearer once the computer has been evaluated and the proper course of action determined.

It is fairly unlikely that the root cause of this problem is faulty hardware, so I imagine that you will find the problem occurs regardless of the USB port to which you connect the device. The likelihood of all USB ports on your computer having a hardware fault is very remote, so the more likely explanation in this situation is a software-related issue. The second procedure which we should try is completely powering-down the computer and then restarting, to clear any potential hardware or software related errors. Shutdown the computer and then unplug the power cable from the computer. Leave the computer for 10 minutes, as this will allow time for the temporary memory stores on the computer motherboard to fully discharge and lose their contents. Reconnect the power cable to the computer and start the computer. Once the computer has finished starting, try connecting the USB devices to the computer and check whether the problem has been resolved.

Should the problem continue, try to trigger Windows to manually recognise the USB device. Connect the device to the computer, and you should receive the usual “USB device not recognised” message. Go to the “Start” menu > “Run” and type “devmgmt.msc” then press the OK button. The Device Manager window should open. Select your computer which should be at the top of the device tree. Go to the “Action” menu > “Scan for hardware changes”. This will tell Windows XP to scan the computer for any new hardware devices. Once the re-scan has finished, check whether the device is accessible. Since these are storage devices, the best way to check would be opening My Computer and see whether the device appears.

If the scanning for hardware changes does not detect and install the devices it is possible that another USB device on the computer could be conflicting with the storage devices being connected. To eliminate this possibility, disconnect all other USB devices from the computer with the exception of the essentials (which should really only be the keyboard and mouse). Once this has been done, restart the computer and then try connecting one of the storage devices to check whether this has fixed the problem. If the problem no longer occurs, you now need to determine which of the other USB devices is causing the problem. This is going to be a trial and error process of connecting one of the devices and checking whether the problem reoccurs. Once you have localised the problem device, then you should leave it disconnected for the short-term whenever you wish to use one of the USB storage devices. However in the longer-term, you may wish to conduct some investigations into ways to fix the problem such as connecting that device to a different USB port, or searching to see whether anyone else is experiencing the same problem and has a resolution.

Another possible cause of the problem is that the Windows power management is interfering with the USB ports. Windows attempts to conserve power by turning off power to the USB ports when they are not required, as this can assist in prolonging the battery life particularly in laptop computers. However, it has been known to cause problems. As part of the troubleshooting we will try disabling power management on the USB ports to see whether this makes a difference. Go back into the Device Manager (as explained previously) and expand “Universal Serial Bus controllers”. Underneath this category the USB Root Hub devices will be displayed which are the devices inside the computer controlling the USB ports. Right-click on one of the USB Root Hub devices and select “Properties”. In the Properties window that appears, click the “Power Management” tab. Untick the option “Allow the computer to turn off this device to save power” then click OK to save and close. Repeat this procedure for all of the USB Root Hub devices listed in the Device Manager. Once this has been completed, restart the computer then try connecting the problematic devices to see whether the issue has been fixed.

In the event that the problem continues after disabling power management on the USB Root Hub devices, before proceeding any further you should return into the Device Manager and re-enable power management on those devices (so they are restored to their previous state) as there is no advantage in leaving this setting disabled if it does not help resolve the problem. The next procedure involves reinstalling all the USB controllers in Windows. This should fix any potential problems relating to the USB drivers or other software which interacts between Windows and the USB ports on the computer. Go back into the Device Manager and expand “Universal Serial Bus controllers”. Go through each device under Universal Serial Bus controllers, right-clicking on each device and selecting “Uninstall”. In the confirmation window that appears, click OK that you do want to uninstall the device. Once all of the devices under “Universal Serial Bus controllers” have been uninstalled restart the computer. Upon restarting, Windows should detect the USB controllers and automatically recommence installing the devices. This could take a few minutes, but once the dust has settled after the reboot, and it looks like all of the devices have reinstalled, you can verify that all of the USB controllers have been reinstalled by opening up the Device Manager and checking that there are no yellow exclamation points next to any of the devices under “Universal Serial Bus controllers”. If there are then another reboot should clear those. Once all of the USB controllers have been properly installed try connecting one of the devices to the computer to check whether the problem still continues.

We have now exhausted the common solutions for this problem and should you reach this point and the problem still occurs then please contact me again for further advice.