DVI to HDMI to no picture?

Hi all... after getting an enormous amount of help from y'all in buying a new graphics card, I'm happy to say that my new X1950XT is on the way and should get here Thursday (newegg rocks). For now, I'm getting everything ready; one step in that process included getting a DVI-to-HDMI cable so I can run my new video card to my Toshiba 32" LCD monitor (32HLC56). I've currently got an ATI Radeon X300 in my box, which does have a DVI output. So I decided to try giving the new cable a test run, to see how the hi-def looks on my decidedly low-def card.

I ran the cable from the DVI slot on my video card to the HDMI port on my monitor. However, when I switch TV inputs over to display the HDMI signal, I get nothing but a blue screen (I can change it to black by going into the TV options menu as well). Is there any step in this process that I'm missing on either end?

I'm running:

Dell Dimension 8400
Pentium 4 3.2 GHz
1GB RAM
ATI Radeon X300 (soon to be replaced by an X1950XT)

Many thanks in advance for any advice you might have to offer!