Ati has only this problem of un-stable drivers. anyway, boot your system in safe mood. and see if your settings are on optimal resolution (which your monitor can support).
have you been using same card on previous drive? also, have you set your BIOS on default?
Intel Core2Quad 2.66Ghz 12MB L2-Cache
4096MB DDR Kingston Hyper-X
XFX 9600GT AlphaDog
Seagate 2 X 320GB SATA2
LG L246WH Flatron 24"