Well,
- Open it up, press down on all chips.. Hard, but not too hard. They tend to work their way out of the sockets because of heat cycles.
- Try it with a different power supply.
- See if the PSU connector is stuck in properly.
- Perhaps your disks have viruses on them? Try it with known good disks (and keep the write protect on and remember to shut down the machine for at least 30sec before you insert the first clean disk)
