JP-J,
PC World's healthchecks are pretty awful to be honest. You'd be far better off spending your £30 on Norton Utilities and do a much more extensive healthcheck yourself in about 15 minutes. Every subsequent check is then free...!
You might want to lift off the lid (provided it's not a laptop) and blow the dust out. There's not much more you can do, bar making sure the cards are seated and the fans are clean. Computers are pretty much solid state bar the disk drives, blow out your floppy drive and the hard disk drives are all factory sealed and dustproof units anyway.
Aq