Help please, I turned the volume down on my car stereo a couple of days ago, when I turned the volume back up again nothing happened, I've followed the instruction manual to the letter.....and still nothing!, I have also checked the fuse supplying the unit and that checks out o.k. along with the fuse at the back of the radio, which is also alright? "Safe" is showing in the display but it will not even allow me to enter the code, any other ideas would be vastly appreciated, dont like driving around in silence. thanks.