Windows 7: Black screen on Alt tabing and quiting games

Ok this is the first imt i have posted her so here goes. I have just installed Windows 7 Ulitimate and since that time i have had a problem with my games which is as the title states i dropped to a black screen when ever i alt tab or quit a game.



My Graphics card is a Ati Radeon HD 4870 X2 and i have the most upto date drivers from there site that came out on the 17th of November but still this problem persists.

The strangest thing is that if i reinstall the driver before i attempt to play my games then there is no problem and everything works fine. However as soon as i turn off my machine or reset it the problem returns.

I have spotted that the display settings are changed every time i install my drivers so that the computer thinks i have two monitors (which i dont) but these rest back to what they were when the computer is reset or turned off.

Any help here would be great

Thanks