With it being 3 years old, it's a possibility.
That's one of the advantages of keeping a PC on all the time - if the CMOS battery backup dies, it takes a long time to notice it. ;-)
But I dunno for sure. It sounds like Windows got mangled too and I don't think just the CMOS battery dying could explain the symptoms.
It might be the power supply too - a weak supply can cause lots of strageness.
HTH. GL!
Cheers,
Scott.