Full screen games causing hard lockups

Okay the problem first. If i start a game and it trys to start in full screen mode The computer hard locks where the only thing i can do is hit the reset button. Now like Battlefield Bad Company 2 it will start fine in window mode and i just hit alt + enter for full screen mode and it plays just fine at high settings. BF2 if i try to start full screen it hard locks but if i start it in window mode it runs fine same as the new warbirds game. I am at a loss as to what would be causing this. I had GTA IV come in today and it installed fine and started just fine in full screen mode but i exited out to watch a movie and when the movie was over i went to open GTA IV again and it hard locks also now. I just don't know. Its a fresh install of Vista and everything is up to date.


ASRock A770DE+
Athlon X2 4000+ 2.1ghz OCed to 2.5ghz
ASUS Radeon HD 3870 X2 1GB 512-bit GDDR3
SATA DVD-RW
SATA 300gig HDD
4gigs DDR2
Vista Home Pre 32bit

 

This is a weird one but since no replies yet I'll throw a bone, bare in mind this is a kind of educated guess seeing this is the kind of thing that happens to me.
First thing I would do is check versions of graphics drivers and CCC.
If upto date then I would adjust the scaling option in CCC, save and then put it back. The scaling option sometimes does weird things to some games.
Or if you've recently updated anything I would look to revert back.

Like I said, just ideas of how I would first tackle the problem, not really advice, more like something to check out.

 

Do you have DirectX 9 installed?

Vista comes with Dx10, but both the games you mention were made for Dx9. 10 is supposed to be fully backwards compatible, but as with everything else computers, what should be happening and what actually happens aren't always the same. Try installing Dx9 from here, then reinstall your games by right-clicking on the installer exe and picking "Run as Administrator..." and see if that makes a difference.

 

I disabled Crossfire and everything works like it should now. Tho i read in alot of places due to the video card being dual core the it needs to run in crossfire mode to make use of both GPU's if not in crossfire mode it only makes use of one GPU.