I had to repave my Windows 7 x64 box last week due to a hard drive crash, and for a while everything was running perfectly but now all videos in Windows Media Center are jerky (the sound is fine, they just seem to skip a ton of frames all the time). This is on the local machine, but the same thing happens when I try to stream to my Xbox. The videos all show fine in VLC and Windows Media Player (however exhibit the same problem in Quicktime). I guess I must have installed something recently (in the process of getting all the apps I usually have running on my PC) that caused this but for the life of me I can't figure it out. I have updated to the latest video driver (and then rolled back to the standard Windows 7 driver), I have rolled back all the other drivers that I have installed (I believe). I have uninstalled all the codec packs (I also run TVersity, so I have the TVersity codec pack installed), and I uninstalled TVersity. Nothing seems to help. I have uninstalled windows media center, and reinstalled it from the Programs and Features. I have basically ran out of things to try to fix this, and am almost thinking about reinstalling Windows again. Any suggestions?

Edit

Specs on the PC (which I figured was unimportant since everything used to work perfectly):

Intel Core 2 CPU 6600 @ 2.4 Ghz
Nvidia GTS 8800
Built in realtek-audio soundcard
4GB Ram

Codecs which are failing: All that I have tried, but at least Xvid, Mpgv (mpeg2 video from a camera), and Wmv (only kinds that I have ready access to).