I know it's not a problem with the graphics card or the monitor or hardware because videos on the internet. Videos on youtube play fine. Even flv downloads from Youtube play fun, but only in the flv player format, not once they're converted. So Winamp, Windows Media Player, Realplayer, Divex, WinDVD, every player I have will not play avis, mpegs, won't even play real DVDs in the disk drive. It just comes up with a black screen where the video should be playing (the audio does play meanwhile), not even any errors. And even more weird, the thumbnails are still displayed when looking at the file, so it's as if the system can read what's on the video, make the thumbnail.. but not play it. Which made me think it wasn't a problem with codecs, since it wasn't giving any errors either, and since it was affecting EVERY player and every final format. A few days before everything was working fine.
But just in case, I uninstalled all the codecs and reinstalled several packs of codecs. Still the same situation.
Ran AVG Anti Virus, Spyware Search & Destroy and Lavasoft, nothing infected.
What could it be? How to fix it?
Any ideas at all would be greatly appreciated.