My guess would be a bad power supply. For the record, tell her to stop turning the power strip on and off-- Really, it's 2003, there's no purpose for that... Just turn the devices off properly, rather than killing power... It's sure as hell not going to protect your equipment, and could be harmful. Put the Mac to sleep from now on, if it ever comes back to life...
Back to the point, there's really no way to test a bad power supply, rather than a) troubleshooting and b) using a power gauge. I suspect this will be a job you'll need to have a pro take a look at. Computers don't die of old age, or more specifically Macs-- whatever is wrong with it can certainly be repaired... the question is, at what price...
pnw