Can you enter safe mode? Press F8 continually when you boot your machine. What was the last thing you did with your machine before you found the error? Have you installed any new...

"0x000000C2: BAD_POOL_CALLER
A kernel-mode process or driver incorrectly attempted to perform memory operations. Typically, a faulty driver or buggy software causes this."
This means that one of...

What's on the BSOD message?
The code starting with 0x0000... would be particularly helpful.

Please read previous posts :P

What i would do to eliminate all possible problems:
>Boot the machine with 1 stick of RAM at a time going from each slot, to see if a bad stick of RAM is causing this, or a bad RAM slot.
>Boot...

What graphics card do you have in your machine? If it is quite a recent one, then chances are 300W aren't going to be enough to power that and all the other components in your computer. Try to use...

What power supply are you using? The problems may lie there perhaps. What's the voltage of your PSU?

What are the numbers and letters on the BSOD? To diagnose the problem, we need those numbers! The numbers we are after are the ones in bold represented by X's:
0x00000XXX

edit: you can also...

Well a BSOD points to either graphics card or RAM. What is your graphics card? And how much RAM do you have?

Do you get BSOD's ? (Blue Screen of Death)

So there is no gfx card instaled?
What type of monitor is it that you have?
Has it got the correct connecter for the motherboard? Check the symbol next to the port that you are connecting it to.

Have you got a gfx card working, or are you running out of motherboard graphics for now?