For starters, what motherboard do you have? Different manufacturers may have different error codes for their motherboards.
Edit:
What I recommend doing first (if you're not scared of messing about with your hardware) Is: Take out your gpu and connect your monitor to your motherboard, you could have a faulty GPU. If that doesn't work, try taking out a ram stick, and try turning on the pc, if that doesn't work, try every possible ram combination you can. (Switching the sticks around and removing one, etc). If you have a spare power supply, swap it with the current one and see if the computer works. There are so many things that could have gone wrong, but if you know the motherboard make and model, you can google the manual and check what the coad means.