I'd agree with Dave. It sounds like the machine just needs a little TLC.

A couple of years of wear and tear plus loads of OS and application patches, firmware and driver updates and additions, etc. can all lead to what you've described. It shouldn't cost a lot to have a computer repair shop do the clean up for you if you're not comfortable with it. There are plenty of local small outfits and I'm sure you'll find a few in your own locale but I know also that places like PC World would also have had a service like it in the past, but not sure if they still do.