Instructions:

1. Press start and select Run.. button.
2. Type "Regedit".
3. Find the key "HKEY_CURRENT_USER \ Software \ Microsoft \ Windows \ CurrentVersion \ Explorer \" and "ThumbnailSize". Doubleclick with left mouse button and enter a value between 32 and 256.

If "ThumbnailSize" is missing, right click on an empty area in the right pane and create a DWORD with the value "ThumbnailSize". Double-click"ThumbnailSize". Choose decimal in the Base section. Enter a value between 32 and 256.

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