Near the battery there should be a jumper to clear the CMOS
Turn the unit off
Move the jumper so clear the CLMOS
Put the Jumper back the way it was after a minute
If you can't find the jumper removing the battery will do the same thing
Just be carefull no0t to break the little plastic pieces on the battery holder
It should have 2 little plastic pieces on one side
Accross from them will be a small metal retainer
Compress it against the plastic holder & the battery should pop up enough to remove it
Wait a minute & replace the battery
Try starting it
If that doesn't work I would suspect the power supply went & took the motherboard with it.
Emachines are usually good computers EXCEPT for the power supply.
I have one I bought years ago that I pulled the bestec power supply out of & put a good one in.
[I put the Bestec in the trash where it belonged]
That unit has been running 24/7 almost constantly with no problems !
OCZ StealthXstream 700W,Gigabyte GA-EP45-UD3R , E8500, Arctic Freezer Pro 7, 3GB G.Skill PC8500,Gigabyte Radeon HD 4850 OC [1GB ], Seagate 250GB SATA II X2 in RAID 0, Samsung SATA DVD burner.