I just got a new XFX 6800GT to replace a Ti4600. The mb is ASUS P4S800D-E. As soon as I hit the power button, it starts making this nonstopping beep. I checked the mb manual which says "long beep in endless loop" means system memory error, but as soon as I put the old Ti4600 back, everything works fine. Has anybody else had problems like this? Thanks for any hint.