Power down?!

Hi all,

My Sony Vaio (VGN-N365E ; going on from 3 to 4 years old) seems to be going through the changes that computers *that* age usually goes through, suddenly developing "personality" and refusing to power on when I need it to.

Ok- So when I pres the power button on, the light indicates that it is receiving power, but doesn't turn on. (No other lights, no whir, no fan- silence). Tried with battery only, AC plug only, and both. After I press the power button, the green "power" light remains on. Only when I A) unplug the AC, and B) remove the battery does that light go off.

This is the second time this has happened. Last time, the laptop resolved on its own. Since then, I don't remember turning the laptop off (except last night), fearing that this would happen again.

I've heard about that one problem might be the CMOS battery (which I'm guessing's the battery that looks like pair of watch batteries. A) how would I check for that and B) how would I replace that?

Thanks!