How to Service (Safety check) a computer.?

Hi, I have a 2004 Viglen Genie Desk-Top computer. I have never got round to servicing it though. I just have had other things more pressing to do. The last time it was serviced was in 2006 by the company I got it from! Yes, not good I know. So I just need a list from somebody on what to check and the tests to do to do a service (safety check) on my computer. Who ever answers first with a good and informal list will get the place of "Best Answer".