Hi There
We do maintenance for several local schools and tend to do the following on workstations annually:
Check all fans and replace if required.
Clean system out (With a compressor)
Check case / keyboard / mouse for damage and wear and tear
Tidy all cables and reseat them all checking the connections fit properly
Turn on all PC's and then restart (Listen for PSU fans failing and Optical drives)
Scandisk and Defrag all Hard drives.
We tend to do this maintenance on the server quarterly and monitor the event logs for critical errors daily.
On the server we also do a quarterly check of all UPS, retension backup tapes, clean tape drives, clean up old exchange mailboxes and defragment exchange.
Depending on the systems you have in place the list could go on for ever !