What kind of video card are you running? Does the video card receive power directly from your power supply? ( one of the power supply electrical leads plugs directly into your video card)
If it does, then my theory is that your power supply is the problem, as newer video cards are very demanding in their power needs and since you mentioned your machine "locked up" I would venture to say that the power supply is suspect, as a failed monitor NEVER causes a computer to lock up.
If you know how, unplug any secondary equipment, that is not necessary for the computer to operate, from the power supply (i.e. CD/DVD drives, floppy drives, any usb sources that receive power from the computer, secondary hard drives, etc.) Then, try to boot the computer and see what happens. If you get a desktop, your power supply is most likely the cause of all of this.
However, your power supply could be too far gone at this point to do anything too, so if you have a spare power supply, or can get one to try, you might go that route, keeping in mind to only plug in the necessary equipment for the test.
Hope this helps.
(Or you could just try the C4 option. Would be easier for me too.

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