I have a Dell Dimension E521 and it will not boot to Dell Start up screen or windows. The power comes on, the power button is lit steady green and the fan runs but the screen is black and enters power save mode immediately. Wont let me run Boot menu or boot to CD to run diagnostics. there hard drive light on the front is flashing. Is this an issue with the motherboard or hard drive? or what else? help me please. im going insane.