On my Windows Vista computer I have various video (AVI) files sorted into folders. When I look in one of these folders the icon for each of the AVI files shows a still frame from that video. This makes it much easier to determine the content of each of those AVI files without having to open the files in Windows Media Player. However, this does not happen in any other folders – instead, the file icons are just the standard Windows Media Player icon. Can you help?

Since you can view the video thumbnails in one folder on the computer, there should be nothing stopping the display of these thumbnails within the other folders as well, so it is likely to be a setting in Windows that we need to change to enable this within the other folders. Each folder can display the listing of files in a different way and these settings are folder dependent. This is useful should you wish to display your photo and video folders in thumbnail view (so that the icon for a particular file shows a preview of that file) but you want other folders to be shown in a listing view (as there is no advantage in displaying folders such as the Windows system folder as thumbnails, since most are program or other binary files which cannot be previewed). However, this can result in inconsistency, such as you are experiencing where one folder displays icon previews whereas others do not. We first need to check whether the affected folders (i.e. those which are not displaying the icon previews correctly) have been set to list the files in a way which will allow them to show a preview or thumbnail of the file contents. Open one of the affected folders and click the “Views” button. A context menu should appear, allowing you to select the view format for this folder. Select “Large Icons” (the small, medium and extra large icon options should also work, but the large icons option is a good size for most purposes). Once this has been done, check whether the problem is resolved. If so, then fortunately this was fairly easy to solve so you will now just need to go back through the other affected folders and repeat the same procedure.

That said, if you are interested, there is a method to apply this setting to all folders on your computer. However, before proceeding be aware that this will override how all folders are currently displaying. For example, if some folders are displaying as list or detail view, then by completing this procedure you will be overriding that setting to display with large icons. However, you can always return those folders to a different view on an individual basis. In other words, this procedure will default all folders to the large icons view. However, if you go back into individual folders afterwards and set their view to be something different, then those settings will stick for those particular folders. If you would like to proceed and apply this new view setting to all folders, go to the “Tools” menu (you may need to tap the ALT key to trigger the display of the menu bar) > “Folder Options”. In the Folder Options window that appears, click the “View” tab. In the “Folder views” section of the window, click “Apply to Folders”. This will apply the current view to all folders on the computer. Once that has been done, click OK to save and close.

However, should you find that changing the view to Large Icons does not resolve the problem then we next need to look at the format of the video files as this could be preventing Windows from showing a preview. In order for Windows to show a frame from the video it needs to be able to natively read the video file so that it can extract that frame. If the files are in a format not understood by Windows then this could explain the problem. However, you did mention that videos in another folder do show their icon preview correctly. As a test, try moving one of the video files which does display its preview correctly, across into the folder which contains video files that are not showing the preview correctly. Once this has been done, close and reopen the folder with the problematic video files. If the video file that previously displayed the preview still correctly displays the preview, but the other files do not, then the problem is more than likely related to the file format of those video files. Check whether Windows Media Player is able to play those video files. If not, and you are using a different media player (such as VLC Media Player) to play the files then this would explain the situation – Windows Media Player is not able to read those files to generate the thumbnails. In this situation you could try downloading the relevant codecs for the videos so that Windows Media Player is able to read the files and thus can generate thumbnails. Without knowing the exact files which you are trying to play I am unable to provide advice on which codecs would be suitable, so you may need to consult the original source of the videos for that information.

In the event that both the moved video file (that was previously working) plus the existing files (which never worked) do not display the icon preview then it seems this is a problem related to that particular folder. In the first instance, we need to ensure that the “Always show icons, never thumbnails” has not been enabled. This setting should globally affect all folders, so it is unlikely that this would be the cause (otherwise no folders would be working at all) but it would still be prudent to check. Go into the “Folder Options” window as previously described and back into the “View” tab. In the “Advanced settings” section make sure that “Always show icons, never thumbnails” is not ticked. Click OK to save and close.

Should this not fix the problem it is possible that the thumbnail cache has become corrupt. Whenever you view a folder and thumbnails are displayed Windows caches those thumbnails. This means that when you view the same folder on subsequent occasions Windows only needs to read the already generated thumbnail from the thumbnail cache, which is much more efficient than having to read the original file and extract the thumbnail. However, if the thumbnail cache has become corrupted then this could cause the previews and thumbnails to stop appearing. To clear the thumbnail cache open the Disk Cleanup utility by going to the “Start” menu > “All Programs” > “Accessories” > “System Tools” > “Disk Cleanup”. Alternatively, you can also type “Cleanmgr” in the Start menu search box. In the Disk Cleanup window under the “Files to delete” heading, untick everything. Then, tick the “Thumbnails” option. This will clear the thumbnail cache. Click OK to commence the operation. A confirmation box will appear asking whether you want to delete these files. Click OK. Once the Disk Cleanup utility has concluded, close the utility. Now, revisit the problematic folders and see whether the problem has been resolved. You may notice that when you open the folders the hard drive chugs away for a while and the thumbnails start appearing slowly. This is normal and is indicating that the thumbnail cache is rebuilding.

However, if the same problem occurs when you open the folders and no thumbnails or previews are displayed then a final suggestion which I can offer relates to third-party software. Some users have reported that this problem can occur after installing other media playing software on the computer. Therefore, it may be worthwhile uninstalling any third-party media players to see whether that makes a difference. That said, making this more complicated to diagnose is that often simply uninstalling the media players will not reverse any potential damage which has been caused, as it is possible that the installation of the software made changes to the Windows registry which has triggered the problem and uninstalling the software may not reverse such changes. People in this situation have found that they often need to do some manual registry editing. However, this will be very difficult (and dangerous) because we don’t know whether any third-party software did actually cause the problem (we are just guessing at this stage) and I also do not know what third-party software is installed on your computer that could potentially cause the issue, so I cannot provide guidance on this problem. Editing the registry is also a very risky business, as it really is not designed for manual editing and changing one value incorrectly can potentially have serious consequences for the rest of the system, possibly resulting in system instability and other things generally not working correctly. Therefore, if uninstalling the players does not fix the problem then that is probably as far as we can venture down this route of potential fixes for the problem.

Of course, the definitive solution to this issue (and most other issues relating to Windows not behaving itself correctly) is to backup all important data that you wish to keep and then reinstall Windows from scratch. However, this is a fairly drastic (and inconvenient) measure which most people do not want to take, unless the problem which is being experienced is fairly serious and needs to be fixed. In your situation if the problem cannot be easily resolved I would recommend that you just ignore the issue, because in the grand scheme of things it is probably not a crucial feature which warrants a reinstallation of Windows to fix.