BIOS gave strange "New CPU detected" message

Following a recent security concern, my computer suddenly started acting very weird and slow, so just to be safe, I quickly shut down with the intention of re-installing Windows, but then something strange happened...

A couple of days later I hooked up a CD drive to reinstall Windows, plus a blank hard drive. To my surprise, when I booted, the BIOS informed me that a NEW CPU had been detected and it was being installed! This made no sense as I have made absolutely no hardware changes. This strange message only ever appeared once.

Since then, my graphics card has also been really strange (even with a clean Windows re-install). The graphics are glitching not only in Windows but in the BIOS right from the splash screen.

I'm wondering if malware could have flashed my HARDWARE?

Thank you Samuria. I've just remembered that my computer's clock suddenly became very inaccurate (by hours) which has never happened before, so this would seem consistent with the idea of the battery having run out. I'm not sure where the battery is or how to replace it, but the clock seems to be keeping time now so maybe it's been recharged by running the machine more?

Thanks guys.

Maybe is the battery but it seems a strange coincidence that the battery failed exactly the same time as my OS died and I had to reinstall.

Sometimes, old PC intermittently run into malfunctionality status. and reset CMOS battery (not really replace it. take it out then put it back later) could help.

my ECS GF7100 with DDR2 is over 15 yrs old. still runs good. but occasionally when boot-up it pop-up "super-user password" which I never setup. I was trying some meaningful or meaningless passwords. but none worked. ECS web no any solution as it's completely out-of-date. hence the PC blocked at boot. No BIOS access.

After tested various solutions, it's found, an easy fix is to remove its CMOS battery, leave it out awhile then put it back. then PC can boot normally again.
It is maybe the time to replace CMOS battery. the PC is too old, no plan to spend any more.

The CMOS glitches which result from battery depletion have caused me no end of problems over the years. Probably because I've left PCs shut-down and disconnected from power for months at a time (we have two homes), when I've returned and tried to power-up again, well it doesn't work. As I type this I have two computers that are dead and replacing the CMOS batteries have not revived them.