So far....
ESXi Install Fails
Memtest86 ran for 23 hours with no Errors
Windows Server 2012 R2 Fails
Windows 7 install starts but on the first reboot it won't come up.
Then I pulled a CPU and half the memory:
Windows 7 still won't boot, but hey maybe the install is jacked up from failing with both CPUs.
ESXi Install fails again...
Pulled the CPU and swapped it for the other CPU...again purple screen on ESXi install.
Arg! I guess I'll borrow some RAM from another system later tonight and see if it could be some odd compatibility issue. If that doesn't work, I'll borrow a CPU from another system and see if THAT works. If all else fails...it must be the motherboard.
If I'm missing anything obvious or stupid...let me know!