You have a system that's 2 1/2 yrs. old, it got old. It doesn't matter the amount of use time. if you hadn't already, be darn sure the innards are cleaned. That way, any "heat build-up won't effect the system, but it maybe too late. The PSU is stressed out and needs to be replaced. -OR- some capacitors are iffy, they need to be looked at. Google "bad caps" to look for conditions of problem caps,---> bulky, leaky, blown, distorted, and/or loose. Run the system with side cover off and if it runs longer or no problems for days/weeks, its a heat issue. Verify the fans are working as in 100%, fans are located in frt. video, chipsets, PSU and case, check them out. It is runs real quiet, it maybe a non-running fan??? But verify, if the fan is multiple speed/RPM capable, it should run slow then speed-up to cool device. Alas, the AMD cpu is NOT heat stress happy. If it runs into heat issues, it will shutdown rather than slowdown like Intel cpus. Further, if it was damaged, the cpu can be iffy operation, unknown condition exists. You may want to check the emachine forum(available?) at the emachine support website and query there or google to see if your model is problematic. AMD makes the nvida chipsets and some mtrbds. could be a faulty one, but solutions could be applied if that chipset is googled for. Also, be sure its OFF, not asleep or hibrating. If you hit a key or whatever action(hot key), it should wake-up but it depends on the system and possible bios setting(or OS setup).

tada -----Willy Happy