Techboy,
Three things
1. You need to upgrade the a8N-E bios to 1005.
You should use ASUS Update V6.07.01
Don't use any older version, since you will have problems with A8N-E
I would recommed you download the BIOS file 1005 and then use the option in asus update to update from a file rather than Internet.
Any version previous to 1003 has compatibility problems with memory.
2. Then go to the nvidia site / drivers and download the Nforce 4 AMD platform drivers - version 6.53.
Then download the video card drivers 77.72 Video card drivers.
but you will have to uninstall all your previous drivers and use driver cleaner pro in SAFE MODE before you install the new drivers
Install in that order.
This is exactly what funky said. but i am repeating.
3. But frankly i think your problem is that your graphic card (i am assuming is an NVIDIA based 6600) is that your PowerSupply Unit is not being able to provide enought power. It needs more power than your ATI
would love to know how it goes. Happy fragging.