Logic board or Disc drive not working?

[lukascene]

Is there a way to tell which one is the problem. I got an old phat model, it powers on and goes to the XMB no problem. The blue light is on steady but there is no disc inside (I can`t even insert a disc, the disc won`t go in). The disc drive doesn`t make any nosie or move. I only get black screen when I try and load/play a demo from PSN. So I`m thinking its either the drive OR the logic board thats messed up. I have switched hard drives but that didn`t help. Is there a way to troubleshoot if the problem is the drive OR the logic board?