Windows 7: Video playback problem (screen brightnes)

I dont know where shoud i put this thread bc there is not section for video. But what im going to tell s not a problem with media center...

I have dual boot xp and windows 7 and when i play movies on xp the screen is fine black is black and i have my monitor calibrated. But the same movie in windows 7 is more grey ...like brigthness is not correct and that only happend when i play movie (on any player it is the same gray effect)... I took screenshot and when i look in windows photo viewer the screenshot is normal ..black is black etc... anybody know what is the problem? I did calibrate my monitor correctly and windows colors are ok ... just appearing that gray problem when playing video...

Thanks.



P.S.
Sorry for my English...