Anyone know how 2 get the Windows Media Player to work again/validate after installing Windows Live 1care?

Installed Windows Live Onecare after a rec from a friend for the antivirus aspect, and after it was up and working, the next time I tried to play a media file I was told that I needed to validate my version of the windows media player. Apparently it did not p validation (?) and I haven't been able to play Windows media files since! It worked just fine before- and I'm not using some pirated computer or anything, just a standard laptop with Windows XP that I KNOW came with a media player. Now I'm screwed. Any help would be greatly appreciated! Thanks!