Why my mac doesn't boot?

I have this Santa Rosa model (late 2007) Mac Book Pro 15". The problem is when i press the power button, the indicator light lights up ( dim) and the superdrive makes its usual sound and that is it. No mac chime, no display.. NOTHING!!. when i close the lid the indicator light brightens up. the adapter is okay, the batter is almost dead, and the batter charges when plugged in ( the orange light). I took it to repair, they highly doubted the logic board failure, then they managed to make it work by changing the left I/O board. after a month the problem's back again. same problem..

thanks guys, very much. yeah i took it back to 'em, they said they only opened it, cleaned it, used HOT GUN and it worked again. and later after couple of days its dead. AGAIN. and Osvaldo, i would love to press any such keys but the thing is it does not start up, i tried all those resetting and firewire boot. It doesn't do anything.

And secondly, i don't think its a hard drive failure, because the thing works perfectly fine, i have all my data. and last time when the thing was dead, i took the drive out and copied all my stuff to another drive. and the drive works fine when i brought back from the repair center.

And if it was a LB problem, how could a faulty LB work again after the use of some HOT GUN?? They even said it was a LB failure first time i took there.. but it was I/O board.

i can give a try, replacing another hard drive, see how it goes..?

and again, i thank you guys for giving you time..