a pic of the mobo in question "would be nice " but;
The first thing I would try is getting a pic of the mobo and and letting us have a looksie at the pins........
Could you get a different ( power supply ) from another working computer ? Making a little note of your connections before trying out. Your power supply could still be dead or dying with the lit light on the mobo*
Trying a working power supply with the pins properly placed might save you from wasting time/money on another mobo.
Changing a mobo is not too difficult if your careful and organized a bit. It is not hard, just need to do it right. I would highly recommend spending the $$ on a power supply upgrade for your emachine ANYWAY. It is well known that most pc's come with barley adequate psu's. Especially Emachines! "I changed mine- " . You can save much on this purchase by buying it online versus retail at any store. Go in staplzs or Best BY, look how much they are charging then try a place online like amazon or newegg. A 350 watt or 400 "maximum" watt- would be perfect for your emachine.
lastly* Emachines rock !!! the newer models since gateway purchased them have much better hardware inside (except the psu ;-( A good psu and keeping it clean inside and they last quite awhile !