Windows 7 (64bit) WMP12 & Media Center broken.

Hi, new user to the forums and hoping someone can point me in the right direction.

Recently rebuilt my computer with Win7 64bit RTM. When I first installed the OS all of my video files would play perfectly in WMP and Media Center. This was great as many are in MP4 format and you all know the hoops we've had to jump through to get these files associated with Media Center in the past.

Pleased at the new functionality I went about installing software. I do development so I installed and patched the following:

Office 2007 (then applied service packs and all patches)
SQL 2005 (then applied service packs and all patches)
VS 2008 (then applied... you get the drill)
SQL 2008 (side by side not upgrade of 2005 as I have to work with both)

Finally, I reinstalled iTunes & QuickTime and a few of the standard web video players (Adobe Flash, etc.)

Pleased that I finally had everything back up and running, I took a break, went to watch a video, and discovered that they were no longer working.

In WMP I'd get (paraphrasing) "Can not play file. Possibly missing codec or file not associated."

In Media Center I'd get "File not found."

This is not just MP4s. It gives me this error on almost everything, even WMV files won't play anymore. (Some AVI's still play, but not all.)

*grumble*

Anyway, I've installed codec packs and 64 bit codec packs, uninstalled and reinstalled WMP and Media Center. Tried removing iTunes and Quicktime. No help.

I've tried other media players and the files will play.

I want to be able to use Media Center, WMP, stream to Xbox, and all the new features. I really don't want to reinstall the whole OS over again (the OS install isn't bad, but getting all those Dev Tools installed and patched and playing nicely takes FOREVER).

Can anyone tell me how I broke my media?

More importantly, can anyone tell me how to fix it?