Thanks for your help Wolf. Yes we got the mute working, it falshes up on the screen as SPEECH. Also tried disconnecting the Speed wire as well which did nothing.
I did buy another head unit from ebay and tried that and it still didn't work. When I put my original one in again it worked for a day.
I sold the one I bought and have had good feedback on ebay so it must have been ok.
I need to try an aftermarket one I guess and see what happens.
Its so weird cos everything is there and working, I can control the head unit and do everything that you normally can do but no sound will come out. Then occasionally I'll start the car and it works! I drive to work and its fine. I turned it off and on and it works. Get in the car after work and then it doesn't work!!! Even though nothing has changed or moved. So strange. I've gone months now without a stereo and its driving me crazy! lol