I don't think macbook pro mini display port outputs sound I think its only video, similar to a vga/dvi ports. run a 3.5mm wire from headphone port into tv, or you can get an adapter as your mbp has optical audio via fibre optic cable also in the headphone port
On a similar subject are there any sensible priced HDMI - Display port adapters that don't cost the earth. From what I can see the best they manage is 720p and are in the region of £150.
Toying with moving my gaming junk out of the lounge and rather than buying another TV connecting the PS3 and Xbox to the mac made more sense.
I'd read somewhere that it does when I was looking around.
I had this issue.
Are you using VLC media player?
In VLC on one of the options along the top (I think audio) there's an option to select output sound through HDMI.
Having said that, dunno what would have happened to get it to work when you plugged it back in again....
I know you've fixed this now but mine did this, you just go into your sound settings and change the output