Well from what you say I'm starting to think the motherboard may be damaged, but let's not give up. I'm gonna need more info.
When you turn a computer on, it does a selt-test called "POST". During POST, basic info about the computer is written on screen, such as the processor type and speed and the amount of memory installed. Does this happen when you turn the computer on? At what point do you receive an error? What exactly does the error message say?