The system starts up but then stops at the ctrl alt delete stage
From here, that could mean several things, so we really need you to define that better.
I understand you feel your new power supply is good, and it might be - should be. But you said earlier there were no lights on the keyboards or mice. That's a red flag for me and I would want to be certain I'm starting the troubleshooting process with good power.
a probable failed PSU fried my old motherboard.
It is not rare for a PSU to be taken out by something it supplies power too. It does not have to be the PSU that fails first. The PSU can be collateral damage. And so can every new PSU you stick in there.
And no, I didn't do a fresh reinstall
Well, this is tricky with a couple concerns. First, if the Windows license for XP installed on that HD is an OEM license, that means it came with the "original" hardware - specifically the motherboard. The ONLY
legal way to legally transfer an OEM license to a new motherboard is if the original motherboard failed AND
you are replacing the motherboard with the identical brand and model number, or the maker's recommended model number if the original is out of production. If you decided to "upgrade" the motherboard in the process to a more powerful and current model, that requires a new license. You can replace everything else, just not the motherboard because that is the "mother" board - the "mainboard".
Software makers, not just Microsoft, view an upgraded motherboard as a new computer, and therefore needs a new license.
If you have a full "retail" license of Windows - then no problems. You can transfer as many times as you want. Just don't have it installed on two computers at a time.
I'm just the messenger pointing out the legal facts.
The other problem with moving that installation of Windows over to a new motherboard is all the drivers for the many devices on the motherboard have changed. Windows is no longer configured to use that hardware. Some is no big deal as Windows can use generic. But some may too specific, causing Windows to choke. So I usually recommend a fresh install when swapping out so many different hardware devices at one time. And besides, with a format, it ensures you are not starting out with tons of orphaned junk on your drive.
(Sorry for all the questions, I'm a mere amateur at this sort of stuff!).
No need to apologize. Asking questions and learning is what forums are all about. I am just sorry I cannot say click this and you are fixed. But when two or more major components from a failed computer are replaced at the same time, it is difficult to determine what happened in the first place, let alone what is happening now. These are one of those times I would like the computer physically on my bench where I can touch and feel it - plus I have lots of spare expendable parts laying around to work with.