SL freeze screen

I just installed a new motherboard and SL id getting strange random lockups
the screen buttons disapere and some objects and avs too.
it lasts about 10 to 30 seconds. im not sure where to look to fix this
ive gotten the newest nvividia drivers (uninstalled the old one first)
reinstalled SL, and checked bios settings....
i think its a video card problem?
the system is:
win 2k
AMD athlon 64 +3500
2048 mem
geforce fx 5600

any ideas?
-LW

today i swaped the 5600 with a gf3 and and its working fine and the 5600 is working fine in the other computer.
i dont know why the 5600 wont work with out freezing in the new computer
?
-LW