someone else on the forums may post with other/better advice as i'm running out of ideas

But i'll leave you with a couple last thoughts re: you tube not playing but media player does

1. I wonder if you could have accidently removed a codec you need. You can try downoading installing the K-lite codec pack has many common codecs

2. Do have your XP install CD? As you might do an XP repair which will repair all Windows file and settings back to defaults which might also correct whatever it is you did

not sure what else other to try. Sorry. G'luck

More likely a malicious program has changed permissons in the registry HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Drivers32 and made them invisible for use even at administrator level.

Start=> Run => Regedit then Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Drivers32

If you don't see a list of drivers you need to right click Drivers32 => Permissions and Edit each user type entry to "Full Control" with "Apply onto" field set to "this key and subkeys".

Once done you should see all your drivers reappear. Restart PC and voila.

Chas