The constant barrage of malware, age and such does such things. And keeping a battery with a burnt out cell can damage the motherboard but the makers don't document that for us.
Your choice as to the hardware issues but you could correct a lot of the issues with a fresh install or by using the restore media. For many this is an exercise about how well they prepared for this day.
BEWARE that some models like the dv6000/9000 and many models that used that design are troublesome. You omitted the model number.
My parents have a Compaq (I think it's a Presario) that is about 4, almost 5 years old. It has Vista, and it's been working fine up until 6-9 months ago.
Slowly settings have been changing on their own- the widows sidebar stopped working (although the file for it is still on the computer- it will not run). Right clicking does not allow you to open images, save pictures, or change certain setting on the computer. Recently, my dad has been receiving emails from my mother's email account- that she hasn't been sending- as well. Some of them are titled, and some have no title- but AVG anti-virus won't allow him to open the emails from her.
The internet is very choppy on that computer- when I use the wireless at their house my computer works fine most of the time, but theirs will disconnect from the internet at random times. I thought for awhile that part of the problem was their battery which has a burnt out cell. The computer works as long as it is plugged in, but as soon as it is unplugged it shuts off. However- with the recent email problem, I'm thinking it must be a virus of some kind.
Any help/advice would be greatly appreciated.