Added ram, video card problem

I added 2 sticks or RAM just now. totaling 6GB. when booting vista or win7 the video card returns an error. It's recognized but doesn't work at all. Taking out the new RAM returned it back to normal. both OSes are 64bit. any ideas?

I think it might have to do with memory timings not matching. I have ATI. Ill try to mess around with the drivers

full specs:

athlon 4200, radeon 1900GT, 2GB at 677 and 4GB at 800 that i'm trying to add. vista and 7 are both 64 bit

Yeah there was a problem with ATI drivers and more than 4GB of RAM. Try the latest 9.3 drivers, they work great.

http://game.amd.com/

you might also want to try using the 4 gb sticks alone and see if you get the same thing.