Directs to do it. Power off and unplug. Press/hold power button for ~15 sec. Open the case and remove the motherboard battery. Press/hold power button again for ~30 sec and then replace it with a fresh 3-volt CR2032 lithium ion battery (right-side-up!), about $2-$3 at discount stores. From the source above.
It just shut off? Or it doesn't turn on? did you move it? Shake it or something like that, maybe it's the them just take it out for few secs then put it back not the greatest help but might be better then saving money.