Do you have an DVI to HDMI adapter on the output of your Video card?
You connected a HDMI cable to the T.V. ?
HDMI cable out to the T.V. through a DVI to HDMI adapter doesn't provide any audio unless you have a SPDIF connector from your motherboard SPDIF out connector (if there is an onboard pin-out) to your Video card SPDIF input.
(This is dependent upon your video card supporting a mobo to video card SPDIF connection.)
Without this you need to provide a HDMI video input and an analog sound input from the PC to the T.V.
What kind of T.V. are you trying to connect to?
I'm using a HDMI/Analog audio input combination on my LCD. Port #6 on a Sharp LC46D64.
I hope this helps.