Christy, I am retired from industrial electronics, and have repaired a few computer power supplies. I know how a standard AT (old type) and ATX (newer type) power supplies. emachines are ATX technology I think, but not sure as I have never seen one.
But for right now, let me tell you a little bit about how an ATX power supply works, and why I don't believe the problem could be the power switch.(well..maybe it could be).
The on/off switch on any ATX type computer acts like a doorbell or horn button on an automobile. It only works as long as you mash it down...release the button, and the bell or horn stops.
In an ATX power supply, there is two supplies in one housing. A 5 volt part that is always on..there is no way to turn it off by a switch. It is powered on as long as the computer is connected to the AC power source, i.e. the wall plug in socket.
This extra 5 volts is used to turn the main power on and off by way of the case "momentary" switch...if this switch goes bad, it will not turn the computer on or off..unless it is partially shorted, and the computer remains in the off position and held in this state until all power is removed and the circuits are returned to their normal state..then by re applying the AC power, the system will again turn on.
I have only heard of this happening one time, but that may be exactly what is going on in your friends computer..if in fact an emachine follows ATX technology.
If that emachine has a reset button, have some one (or yourself if you are hardware able) swap the reset switch for the on/off switch..they are identical switches and exchange readily. If this fixes the computer, then try to replace the switch with a generic one if a direct replacement is not available.
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