ATI Asus HD4890 WTH ?

Hey evry1 , just swtiched to a ati card and and i dnt understand why it can run some games without a probleme (Crysis,Dirt2,Burnoutparadise...)and some other games(Borderlands,CS 1.6) well lets just stay a weird unidentified thing happens.

What happens is whn i run the game the screens blanks off completely like if no power was running threw it but i can still hear the sound of the game running just no image at all ! The only way to get the screen back on is to blindely press Alt+F4 (to close the game)thn take the plug off and replug it.

Now i thought the probleme didnt come from the card or the game, because just before i did a clean install of win7 the games (MW2 ,Borderlands.CS1.6)were running fine. I just did a clean install so i could get rid off the leftovers of the nvidia gpu drivers, because Ati CCC couldnt run and driversweeper wouldnt install in my pc for some weird reason.

So after my clean install of win7 reinstalled evrything back to hw it was drivers(i have a nvidia chipset so i had to install nforce and physicx for some games because otherwise the game wont lauch at all or run really badly Mirrors edge and MW2 for instance ), but this time CS and borderlands had tht weird probleme !  

This is my 1st ati card so im not sure if i missed out some drivers or softwares or .... coz this is the only logical explanation i can come with .
Working before clean install then not working after clean install WTH !  

I would much appreciate your Help to solve this issue .
Thx in advance  


Specs:
Intell Quad Core Q6600
Asus P5N-E SLI mobo (Nvidia Chipset)
Corsair TX650
HP w2207 HDMI
Ati Asus HD4890
2GB DDR2