Radeon 5770 HDMI output doesn't work

My machine is fitted with a Radeon 5770 video card. I normally connect to my monitor via the dvi output with no problems. However when I noticed that both the monitor and the video card have HDMI ports I tried connecting with a HDMI cable. The result was a "No Signal" error on the monitor and no video as a result. What have I missed out on here?

Thanks in advance for any help

Cheers

you have to change the settings in windows and the ati catalyst control center settings?
HDMI - Wikipedia, the free encyclopedia
HDMI and Computers
http://www.youtube.com/watch?v=q0t3FjONb4s

Set the card up to connect to "HD TV" @ 60hz? in catalyst.

Check same in WIN 7
> right click screen
> screen res
> "1920x1080" (this res. ONLY if your monitor can cope with this - otherwise you could bust it)
> next - "advanced settings"
> monitor = 59/60hz

Easiest way >
Uninstall then reinstall Ati driver with HDMI lead only connected. It should detect HDTV/do all this automatically for you!

Reset your monitor if you have messed with the settings as menus will usually revert to "Auto-detect" incoming leads!

That should do it.

Fill out system specs for further help - Ta
Can you at least tell us your monitor make/serial - or is it a secret?

Thanks for your help. Problem solved.

Cheers