Well there's your problem then. VGA output produces an analog signal. DVI demands a digital input. You can't make the two talk to each other properly with a cable. You must either use the VGA input on the monitor or buy yourself a new graphics card with a DVI output. The cable you bought off eBay is for the reverse of what you want - DVI out of the tower and VGA into the screen because you aren't trying to improve the signal that way, simply degrade it.
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Do you know that we're all in line for succession to the throne? Really?
Well, if forty-eight million, two hundred thousand, seven hundred and one people died I'd be Queen.