power to computor emachine 420 running xp?

Fans stopping, especialy if it include the power supply fan, mean that the power supply disjoncted, usualy from overheating.
It looks like there is a problem with your power supply. Initialy, it was probably only overheating due to dust buildup, but, over time, that heat seems to have caused some other damage.

If that's the case, you need to replace the power supply. Chose one with approximatively the same power rating as the original one.

You may also have dust buildup on the CPU heat sink, or it's fan no longer work.
Open the case. Using a can of compressed air, blow away any dust in the CPU heat sink. Power up for a few seconds to see if the fan do work. If it don't work, replace the fan.

Electro
November 2012