Css crashing with crossfire

hey guys,

i am having a problem with my system, it is onlt applying to any game run through steam, every other game i have works perfectly

these are my specs

core i7 975 extreme 3.33GHz
asus rampage 2 extreme mobo
12gb corsair 1600MHz ram
3 x Ati HD5870 1GB Graphics Card in Crossfire
vista ultimate 64 bit
latest graphics drivers available

what is happenig is i will load a game from steam lets say counter strike source and as soon as i change the detail level, even the slightest change the game crashes, i can adjust the resoluton perfectly fine but not the detail level.

and then if i reduce my crossfire setting from 3 GPUs to 2 GPUs the game doesn't crash but it glitches something shooking but if i disable crossfire it works perfectly fine and completly smooth

can somebody help?