About every 6 months I do a clean install of the OS. When it gets too bad I remove the various fluids and food particles from my keyboard and surrounding area
Occasionally the PC/monitor/modem get a wipe with a damp cloth. I check for viruses and new patches on a weekly basis. I run a Spyware scan when I remember to. Scandisk and defrag are tricky - the PC has to be in safe mode otherwise they won't run. They're done on a roughly monthly basis.
PC World should be shut down - they're an embarrassment to the profession, preying on newbies and family users.