DVI can be analogue or digital depending on the output. Most gfx cards today have DVI-I outputs which can output digital or analogue signals. But in some cases, e.g. the new Geforce GTX 680, you have two DVI outputs. But only one of them is DVI-I, the other one is DVI-D which have just the digital signal and isn't compatible with dvi -> vga adapters.
I see that you've fixed your problem, but I'll just add another possible solution for people with the same issue. If you get a black screen like described here, you can try the "enable vga mode" option in the Windows boot menu (same menu you use to start safe mode). This will boot Windows normally, except for setting the resolution to 640x480 which pretty much any monitor should handle properly.
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