All very interesting and techy, but can we assume that the OP has checked the obvious?

Worth a try, but disconnecting the HD cable(s) and firmly reconnecting can work wonders. Not rocket science, but vibration from the fans and the disc itself can cause connectors to work loose over time. Ditto the RAM.

I was conned by a techo into buying a new PC when I had a similar failure and message. A year or more later, I gave the old PC to a friend who did just that, and it powered up no problems. Still using it 3 years later....

Not saying that the OP shouldn't upgrade. Unfortunately XP has had its day and likely to fail eventually, but still useful especially for off-line tasks and with all those wonderful programs that W10 or Linux doesn't like.