Loud Fans, Black Screen, No Startup Chime, No 3rd LED, HELP?!

I bought a second hand mac from an older guy that wasn't working when I bought it. I thought being fairly handy with computers I might give it a go- it was a very cheap buy and as a last resort I believe I can part it out and still make money.

The iMac is a 2.33 20" Intel Core 2 Duo Machine. When I bought it, I plugged it in and all that would happen when you powered it on was the white light would come on, the fans would immediately turn on full blast, and that was it- fully black screen and no startup chime. Here's what I've done so far...

1. Resetting SMU by unplugging and plugging back in- no luck

2. Replacing the RAM with brand new ram- no luck.

So after that I took the lcd off to gain access and noticed the PRAM battery holder on the logic board was broken- a battery was loosely taped in with electrical tape. So I went out and bought a brand new battery and tried to boot the computer while holding the battery in place with my finger. Still the same thing happens- no 3rd led and immediately loud fans...

I've been doing alot of research and it seems like I might have a bad logic board but I hate to just give up at this point. I've now removed the harddrive and I was going to put it in an enclosure and see if it boots.

What else should I do? It is fully out of warranty (5 year old machine). Are there some other trouble shooting steps before I just part it out?

Thanks!