On my Media Center PC, after reinstalling some video codecs, my MKV* video files made Windows Explorer crash regularly when opening a folder with one of these files in it. To solve this problem, I had to disable automatic thumbnail generation in Vista or Windows 7. Disabling thumbnail preview in Windows Explorer can make Vista/Windows 7 perform notably faster in any case, as Explorer will no longer be generating thumbnails for every video and image file in every folder you open. This is especially useful when browsing back and forth between multiple folders. Follow these steps to disable the automatic thumbnail generation:

  1. Press and hold the Windows key on your keyboard, then press E to open Windows Explorer (alternatively click Start > Accessories > Windows Explorer).
  2. In the Windows Explorer window, click on the Organize button on the menu/shortcut bar.
  3. In the pull down menu, click on Folder and Search Options.
  4. The Folder Options dialog window will appear. Click on the View tab.
  5. Under the Files and Folders tree heading, check (tick) the box next to Always show icons, never thumbnails option.
  6. Click the OK button and you’re good to go!

* MKV is a common container format for video, audio and subtitles, often used to distribute standard and high definition video, audio and associated subtitles in one single file, with support for multiple audio and subtitle tracks, just like on a DVD.

Edit: Some newer codec packs, such as the Shark007 Codec Pack, by default turns off MKV thumbnails, but also makes it possible to easily control this and MANY other settings through an easy to use Windows application interface.