iMac g3 shuts down

My Bondi Blue iMac g3 shuts down after maybe 10 minutes, then after I turn it back on, it shuts down quicker and quicker each time. Could it be overheating? It doesn't feel hot and the fan is running.
Terri

It sounds like the power supply cuts out after a certain amount of heat buildup. This is probably something that would need professional attention; however, the cost of repairs would almost certainly exceed the cost of a used G3 iMac.