Hi, I've been searching and trying solutions for a while now, but I have to get this computer back to the grad student soon and I'm running out of options.

I'm getting a stop code 0x0000001A when trying to boot/install Vista.

System:
OS: Vista Enterprise x64
Computer: Dell Optiplex 745
RAM: 4GB

Issue:
I'm having trouble running Vista x64 with 4GB of ram. I tried to install Vista with 4GB of ram, BSOD. I take two sticks out (doesn't matter which two) and try again, installs perfect. I reinstall the 2GB of ram, BSOD. We have SP1 already installed and I updated everything before reinstalling the other 2GB of ram. This problem reminds me of when I had to install with 2GB of ram on my personal machine, then do the hotfix, then reinsert the other 2GB of ram. They supposedly fixed that with SP1 though.

Things I have tried:
Tested the ram thoroughly with Memtest86, Memtest86+, Dell Diagnostic Disc and PC-Check. All report that the ram is working fine.

Tested the whole system with Dell Diagnostic Disc (All but the interactive ones). Reported ok.

Swapped the power supply with another Optiplex 745, same issue.

Updated the bios to the latest version for Vista x64.

Reseated all connections on the motherboard.

Run chkdsk /r.

Reinstall multiple times.

Tried installing that "Installing with 4GB" hotfix, but it doesn't apply to this machine. (I assume because I already have SP1 installed)


Notes:
This is the first time I have run into this issue after installing this on multiple other campus machines. I want to say it is a motherboard issue, since this is one of the first Optiplex 745s we purchased and the newer ones (with different motherboard revisions) don't seem to have this issue.

If anyone has any ideas or has solved this issue, please help me out.