I have an ATI Radeon HD 5450 graphics card (512 MB) in my HP Pavilion Elite. The graphics card has two ports--a DVI and an HDMI. I have two monitors, both VGA. I have no problem connecting the VGA monitors to the DVI port using a DVI-to-VGA adapter, but I cannot convince my computer to recognize either monitor through the HDMI port.
I've tried two solutions--one was a simple splitter from the DVI port, which as I expected displayed both monitors but only as clones--it would not do an extended display. The second was to add an HDMI-to-DVI-D adapter onto the the existing DVI-to-VGA adapter. I thought this might work, but the monitor doesn't detect a signal, and now I'm not sure if it's because the principle is wrong (i.e it is impossible to convert to a VGA signal through the HDMI port) or because my HDMI-to-DVI adapter is bad. It seems like, if the card can convert to the VGA at all, it shouldn't matter which port I'm using, but I'm not sure.