4870x2 issues

So I finally decided to overclock my 4870x2 and this happens, I go into catalyst and it works fine it lets me overclock the card so then i start GTA4 and it goes to and stays at a blank screen and does nothing so i have to reboot my comp. It does this with every game ive thrown at it, i mean i i dont overclock it it works just fine with manufacturer clock settings but Ive got an i7 965 extreme CPU 6GB of tripple channel ram a 500GB HDD and a 650W PSU all on a DX58SO mobo so i wanna see what my graphics card can do. If any one has any ideas of what the problem may be please help!