Every time I logon to the internet the computer hangs. The start bar still works but if I try to click on a program nothing happens. The only way to unfreeze the computer is to press CTRL-ALT-DEL numerous times (sometimes for up to a minute of continuous key presses) until the Task Manager finally appears and everything then works normally. What is happening here? The computer is running Windows XP Professional.

When you say that you open the Task Manager and everything works ok, I assume that you are not closing any particular application/process using Task Manager. If you are, then this is likely to be the problem application, so all you need to do is close that application before logging on to the internet. On the other hand, if the computer returns to normal when Task Manager opens (and you do not take any subsequent action within Task Manager), chances are that Task Manager opening has nothing to do with unfreezing the computer. Instead, when you press CTRL-ALT-DEL the computer is already busy doing something else (which is causing the computer to seem to be frozen) so it cannot open Task Manager. However, once the computer has finished doing its mysterious task, it has the resources to open Task Manager. Thus, Task Manager appearing is a signal that the computer is unfrozen. My theory is the reason for the computer freezing is some application is attempting to access the internet as soon as you are connected and it is causing the whole computer to freeze. In order to diagnose this problem, you should try closing down all non-essential applications before logging onto the internet. Close any applications running in the background, including in the Windows system tray, and then use CTRL-ALT-DEL to close any programs which are not visible. If the problem ceases, then each time you logon to the internet close one fewer program until the problem resurfaces, at which time you will know which application is causing the problem.

In the event that the problem persists even with all applications closed, then the cause could be due to some issue in Windows itself, such as the networking protocols or some unknown factor. In this situation you may wish to try reinstalling your modem drivers and, if all else fails, reinstall Windows (although this is not the most elegant solution).