i'd second getting it checked out. if it's not an easy fix (reseat ram, try another ac adapter, remove battery) it's probably something internal. if you have another stick of ram, no harm in trying that. also removing the hard drive and seeing if that allows you to at least get a power light.
did you inspect the ac adapter receptacle? sometimes the pin(s) in there can get damaged. i've even had one come out and stay in the cord.