So you got the original RAM with you

I want you to do a verbose startup. I assume that you still hear the chime. To do this , press Command + V

So its completely out ?

Tried resetting PMU and those stuff as per in apple site ?. Did you make sure that your rams are attached properly ?

If you have tried all the basic troubleshooting and still can't get it to boot up. Chances are you have messed up something !

For Intel Macs

Yes , both FireWire and USB CD-ROM/DVD-ROM would work and you're able to boot from it as well

This is where the knowledge of hackint0sh kicks in. It helps mac users , but they are in denial anyway. Nevertheless , boot your mac with command (apple key) + v , before the chime. I strongly recommend you to use verbose

This is because when you shutdown , it will switch to verbose which should give you an idea why its hanging. Its most likely caused by incompatible kext and other things. It will give us a clue. The reason why it does not shut down is that its waiting for something , itsj ust that the "process" is in deadlock

Just boot off from a cold boot

press command + v before the chime and just hold. If you did it properly , the spinning apple logo will change into some DOS like thingy with a lot of text where you can read

once it has booted , just shut off

Instead of going through normal shut down , it will show a similar thing , from there we can find out whos the culprit