Something is wrong.
It is not likely to be a lack of cpu support in the bios because the pc has been working for a long time.
I would not try to update the bios, particularly with a flaky system. A failed bios update can permanently render your motherboard useles.
What has changed?
Possibly reseating the cpu could fix the problem as iceclock suggested.
Or, see if you can run memtest86+ to check out the ram.
It does not use an os and boots from a usb, cd, or floppy.
I have a memtest86+ cd. then tomorrow first i clean his cpu and then remove the comose battery and third test the ram using MEM test86+