CPU Only Boots Once?

[JohnDN]

I modified a Xeon E5405 to work in my EVGA 790i Ultra motherboard.

After removing my Pentium D 925 and installing the Xeon, it booted just fine into Windows. However, after restarting the computer I get a post code "AA" on the motherboard LCD display and nothing POSTs on the monitor. Clearing the CMOS, or removing CMOS battery does not fix this. I have to install the old Pentium D, boot and then shut down and install the Xeon to get it to boot with the Xeon again.

Experimenting, I discovered the following items:

Booting Xeon into windows shutting down = code AA next boot.
Booting Xeon into windows restarting = code AA next boot.
Boot Xeon, entering BIOS settings, exit WITHOUT saving = reboots ok
Boot Xeon, enterting BIOS settings, exit WITH saving = code AA next boot.

When reinstalling the Pentium D 925 to get it to boot so I can experiment with the Xeon again, I discovered that...

Pentium D must reach the Windows loading screen for Xeon to work next time
or
Pentium D must enter BIOS settings and exit WITH saving for Xeon to work next time.

One of those two things must happen, if I just put the CPU in and let it POST, or enter BIOS settings and exiting WITHOUT saving, the Xeon won't work next boot.

Apparently, something in the BIOS changes when you enter the BIOS even if I don't change any settings or if I let the computer reach the "windows loading" screen because the Xeon won't boot after that, but it will reboot if I enter the BIOS and exit without saving.

The EVGA P10 bios has microcode for this Xeon processor built in (revision C) I updated the microcode in the bios to revision F, but it didn't help any.

Is anyone familiar with what the BIOS does when it detects a new CPU and what I can do to correcy this problem?