Simple things first:
Unless it is the Hard Drive failing, do not worry about loosing stuff. All you need to do is to take out the old hard Drive and put it into a suitable Enclosure (About £15) which will turn it into a External Hard Drive, you can then read the contents at your leisure.
My first impression is that it might be over-heating, which could be caused by fluff which can block or restrict Air Ducts. So a good clean out should be ones first point of attack.
There are so many ways of doing this that you can make up your own. Suck it, blow it, briskly brush it, remove the covers and scrape it. Or in my Niece's case, peel it ~ She'd been using her Lappy on the sofa and the intake was full of Dog Hairs.