It's understandable that your problem has you frustrated. But you should remember that no one here gets paid for any help they offer, and Oldtimer did try to help you.
Anyway, I would suspect a corrupt DirectShow filter. The fact that VLC still works would tend to confirm that the problem lies there. You can view your codecs with CodecSniper, and see if any are "broken". Free, get it here:
http://www.videohelp.com/tools?tool=Codec_Sniper
Careful what you delete with that! In the listings, you will see the source, whether it's from a codec pack, for example. (Lots of computers get fooked with codec packs). Typically, those are safe to delete. If unsure, post a screenshot.
Wouldn't hurt to run system file checker as well to replace any corrupt system files. Start -> Run ->
sfc /scannow
Note the space after sfc. If there's no I386 folder on your C drive, you'll need your Windows CD handy. (This pertains to XP).
One more thing. You don't specify what types of videos are giving you problems, or maybe all of them. This may or may not be applicable: It's not unusual for downloaded vids to have corrupt headers, which can give Explorer fits. Most times one can fix that by running something like DivFix on the file, or running it through VirtualDub on direct stream copy to rewrite the header. But I'd try the other things first.
Good luck.