HOW CAN I CODE MY CORSA STEREO?

I tried to code the stereo in on my sons corsa sxi 02 plate after it was taken into the garage for repair. I have read the manual and tried to code it in 3 times but found I had the wrong code. The screen shows "7 SAFE". I have now paid and had the code sent to me but I cannot get the stereo to the stage which will allow me to put the code in. The screen just shows 7 SAFE. Can any one help?