Q: no sound in hdtv after connecting via thunderbolt to hdmi cable from macbook pro

Is the accessory that you bought "Thunderbolt to HDMI", was this purchased as an Apple accessory or 3rd-party?

What model MacBook Pro?

The mini display port on earlier Apple computers only support video. See:

About Mini DisplayPort to HDMI adapters

Also, if you go to System Preferences>Sounds>Output do y see HDMI or Min displayport as an Audio out option?

If your MBP is a model prior to 2010, it does not support sound via HDMI.  You will have to tap the audio output port with a separate cable.

Ciao.