I have a Blaupunkt 300 , in my Astra MRk4. It's gone to safe mode, I have ?

I have a Blaunpunkt 300 cassette radio , in my Astra mrk4.it's in safe mode, I have taken the advice of people on here, and left the radio on for over 2 hours, only to return to it and it has turned itself off.therefor Iam unable to enter the code. I am I missing something?