win xppro boots to bsod, reinstall won't fix

I have two pcs I'm working on, both win xp pro. One I built, one is HP Compaq. Both have been off internet for more than a year and running well.
One day, the hp came up with bsod. I considered: virus, memory, hd, os glitched, mobo.
This is what I did as testing: in hp pc, new hd, fresh installed xp from cd. Install proceeded normally thru final reboot, then bsod. cold boot, restart, safe boot, all bsod.
Didnt have mem stick or mobo, so tried fresh install on this new hd of win 7 pro, to test hardware, and all went well.
Next, same hd, installed Ubuntu 17.10.1, no problems either.
I'm thinking these two tests prove the hardware is ok.
Next took the new hd to 2nd pc, one I built. Fresh installed win xp pro from same cd as before, install went well, no issues at all.
Next, I put this hd into hp pc as-is, and tried to boot. BSOD.
HD back in other pc, boots normally.
Next, with my other pc up and running win xp pro on its own hd, I connected original bsod hp hd as external usb drive and tested it with scandisk, no errors, then for viruses with avira free. I got 85 hits trcrypt gen3 trojan, found in downloads from ms update and google update. cleared them, reran with no further hits.
Put this hd back into hp pc and bsod!
Question is, can mobo/bios rom be causing this due to xp, yet still run win 7 and ubuntu with no issues?
Or????? HEEEEEEEElp!
thanks, seekertom

2/6/18,adding bsod info: stop: 0x0000007B (0xBA4C3524, 0xC3524, 0xC0000034, 0x00000000, 0x00000000)

i replaced mem stick. its a single 4gb stick, and have tried it in either slot, still get bsod after windows completes last reboot. to restate, i've tried different hds and different install disks/keys. what still strikes me is the fact that the new hd boots all during the install process, except for the final time.
thanks again for the help! st

This might help you along towards an answer.. it's a bit long for a comment.. It does address some of your questions..

I have two pcs I'm working on, both win xp pro. One I built, one is HP Compaq. Both have been off internet for more than a year and running well. One day, the hp came up with bsod. I considered: virus, memory, hd, os glitched, mobo.

ok

This is what I did as testing: in hp pc, new hd, fresh installed xp from cd. Install proceeded normally thru final reboot, then bsod. cold boot, restart, safe boot, all bsod.

Didnt have mem stick or mobo, so tried fresh install on this new hd of win 7 pro, to test hardware, and all went well.

Next, same hd, installed Ubuntu 17.10.1, no problems either. I'm thinking these two tests prove the hardware is ok.

So some issue with XP Pro on that hardware, whereas other OSs run OK on it.. Some conflict.. we don't know what.

It could be a hardware issue on the HP PC, that XP Pro is tripping up on and the others are avoiding.

You could experiment with installing off a different medium e.g. XP might install off USB https://gadgets.ndtv.com/apps/features/how-to-make-a-bootable-usb-disk-for-windows-8-windows-7-windows-xp-649811

But probably will BSOD.. as it has before.. It'd help to see the BSOD error. You can take a photo of it with your phone.

Next took the new hd to 2nd pc, one I built. Fresh installed win xp pro from same cd as before, install went well, no issues at all.

ok

Next, I put this hd into hp pc as-is, and tried to boot. BSOD. HD back in other pc, boots normally.

Well that particular BSOD is to be expected.

You installed Windows on the 2nd/built PC, and that one wasn't meant to run on the HP.

Next, with my other pc[the built one] up and running win xp pro on its own hd, I connected original bsod hp hd as external usb drive and tested it with scandisk, no errors, then for viruses with avira free. I got 85 hits trcrypt gen3 trojan, found in downloads from ms update and google update. cleared them, reran with no further hits. Put this hd back into hp pc and bsod!

may be irrelevant though 'cos you get a BSOD on the HP with a fresh hard drive too.

Question is, can mobo/bios rom be causing this due to xp, yet still run win 7 and ubuntu with no issues?

Could be something on or connected to the motherboard that XP is clashing with and the others aren't. You could try Safe Mode.

There are various things you can change.. If there are two RAM sticks just run it with one RAM stick.. You could even try a different CD. A different CD Drive. different build of XP Pro, different ISO.. different hard drive cable, different cd drive cable. Safe Mode. Installing off USB (Which a link suggests is possible with XP). Take a photo of the BSOD error.

I have had USB-PS2 adaptors that have been very odd in terms of conflict.. just little things that don't even require any drivers. But one of them worked in all my computers. Another one worked in one computer and not another. I had two computers and two USB-PS2 adaptors. So I figured I had one computers that was very compatible with USB-PS2 adaptors, either of them worked in it. I had one USB-PS2 adaptor that was very compatible, it worked in either computer. I had one computer that was very strict and would only accept one of my USB-PS2 adaptors. And I had one USB-PS2 adaptor that was very strict, only worked in one computer. I chucked out the USB-PS2 adaptor that was strict(not so compatible). I once had a computer where only one monitor would work with it. So its VGA card must've been ridiculously strict. Somebody was happy to buy it off me even knowing that, and I was glad to get rid of it.

When it comes to compatibility problems, many things are possible! Including incompatibilities that you'll have not read about. But you only really know when you've troubleshooted it down to finding out exactly what it is! The exact BSOD will help shortcut that.