|Power supplies can fail in many ways. The Green light on the MOBO is only 1 indication of Power available to 1 Part of the System.|
Considering that this is an eMachine (i have 5) I would suspect the Poewr supply has failed.
CEASE trying with the original Power supply or you could loose the Motherboard, if you have Not already.
Pull the PSU and either have it tested or swap in another PSU (not Bestec) of the same Power ratings to see if the Computer will Start.
Resist the temptation to buy the cheapest PSU you can find. You get what you pay for.
There is nothing to learn from someone who already agrees with you.