I did research on this a while ago, and here's what I came up with. When you look at the signals going over the cables from your graphics card, there are basically two types - analog (vga) and digital (dvi, hdmi). Converting from one to the other requires an active adapter. Fortunately for you, dvi is designed to have backwards compatibility, and has analog signals flowing alongside the digital ones. The adapter you have most likely just connects these signals to a vga connector. Unfortunately for you, hdmi doesn't have these backwards compatible signals. So you can go from dvi to vga, or from hdmi to dvi, but you can't go from hdmi to vga with passive adapters.