HDMI connection to HDTV

I have contacted Dell to ask this question but since I have upgraded Vista from Home Premium to Ultimate I was told I had voided my warranty. I have a XPS M1530, when I plug in the HDMI cable to the computer and Sharp 32' Aquos HDTV, it is recognized on my NVIDIA control panel but I do not get any image on my TV. I have set it up as a clone display. Any suggestions on what I may be doing wrong?