All right, I've got a pretty strange one here. Since I installed Windows 7 on this machine some time ago, image thumbnails have never worked properly. For the vast majority of images, they completely fail to show up, showing the icon of the default image viewing application instead. Please note that the “Always show icons, never thumbnails” option in folder options is not checked. I've taken a screenshot demonstrating the problem, here:

Sometimes, a few image thumbnails will show up correctly, maybe about one in ten, with the rest failing as well. Another screenshot, with a handful of thumbnails visible, can be seen here:

Windows explorer does not appear to make any effort to populate the missing thumbnails, and there is no appreciable CPU usage. I can leave a window with missing thumbnails open all night and they will still never appear.

Newly created images never generate thumbnails, only images that have been on the system since day one will occasionally show them. This leads me to believe that explorer is set to show thumbnails, but whatever process is supposed to be in charge of actually generating them has failed somehow. In previous versions of windows, explorer.exe itself was responsible for thumbnail generation – has this changed?

Any suggestions at all – even if you aren't sure that they will work – are welcome. I'd hate to have to wipe and reinstall on this machine for such a minor annoyance.