I'm rebuilding a HP Pavilion Desktop a1200a. All I had to do was add a PSU, Intel 2.66GHz processor and hard disk. These items all worked fine in another PC. One compatibility problem I had was the Psu is 20 pin and M/B 24 pin. After some research I was told it will work and to insert the PSU plug into the M/B on the right hand side of the plug leaving 4 plugs free on the left. I will use on board graphics - there is no PCIe graphics slot.
I booted up to install XP Pro and an error appeared in the post..."Microcode Failure...update bios...call HP" I contacted HP and they didn't want to know except to say I couldn't update bios unless I had a functional O/S. I thought I could do it with USB flash drive or CD..."No" was the answer.
I F2'd to continue out of boot and access CD. Install worked fine right through the process but when reboot time came around I got the BSOD. I've gone through the whole process about 7 times with the same result. Could the fact that I'm not connecting to the M/B with 24 pin power lead be the trouble? It's happened with 3 different hard drives (2 x IDE and 1 x SATA)...every thing happens exactly the same from Microcode failure to BSOD. I could buy a 24 pin PSU but if this isn't the problem it's a waste of money and I don't have access to one to try from another source.
These are the files in the latest windows XP based HP bios update .exe file
I had a brainwave! Could I rebuild my Windows XP installation CD with NLite and slipstream the latest HP bios update .exe file into it?
I once had a bios issue with a notebook where it wouldn't recognise SATA drives. I NLited the files into XP disk and it worked loke a dream.
It looks like your BIOS is not compatible with the new CPU. You could try to update the BIOS with the OLD CPU installed and then try the CPU swap again. Most BIOS updates only need a DOS disk for updates. Does HP only do BIOS updates through Windows? Good Luck