Hard drive activity but no boot, chime, or Sleep Indicator Light

This is a 2.4GHz model. The hard drive immediately spins up upon hitting the power button, but does not go further than that sometimes. Usually has no chime or any other activity what so ever other than just the hard drive spinning up. It sometimes boots normally with chime and apple logo and successful loading of OS after giving it a good 20 minutes of just black screen or sometimes not at all. It needs a new battery. I am only going to order the battery if I can pin point the problem. Is it logic board related? Pram battery related? or just a new battery could solve it.

Appreciate the help in advance.

Well, I can't even get anything on screen to popup, I've been messing around with it for hours now. I took the keyboard off and disconnected the pram battery. Waited a couple hours for the computer to completely empty out power with nothing connected. Hours later with only the power supply plugged in and the pram battery also in, it finally booted. I believe the issue is just going back to the extremely poor quality battery that is the original from 2006. I will order a new one and hope that resolves the problem. I have Lion running happily on the hard drive with no issues.