Problem With Vista-64

I am having a problem with Vista 64 presently. I have tried several clean
installs and cannot seem to resolve it. I have even tried to reset the BIOS
back to the original settings prior to install.
The issue is I get a black screen with only a mouse cursor after I 1) have
Vista update the Windows Experience Index or 2) change to SLI mode, which
worked fine until a couple days ago, when this first occurred.
My system: ASUS P5N-D Motherboard, 4 GB Dual Channel RAM, XfX 8500GT
videocards (2X), 2 SATA hard drives, 2-IDE DVD drives.
The issue first occurred after I had to remove the CMOS battery to reset the
BIOS.

Any suggestions as to how to fix. It occurs in both Safe Mode and in normal
mode and there does not appear to be a way to get past it and get the Windows
Vista GUI on screen.