I have Pavilion dv8 (i think dv8t-1000) have the same no-sound HDMI problem. I tried ALL/MOST of the methods metioned to n0 avail .... UNTILL ..... can you wait for this . ..{partial explaination here} .. I have a cable/tv connection built in the laptop .. in my sound devices set up its called " Sony TV-1 NVIDIA High Definition Audio " after plugging in the HDMI on my TV That I know does both audio&video) .. by the way I have a newer TV that has 2 HDMIs - where 1 HDMI does not do sound from an XBOX ...
... back to my resolve ... I activated -clicked set- as default- the "sony tv device and
TA DAAA ..... SOUND thru my TV thru HDMI ...
** I hope this helps somebody....