87 325e radio reset

My father removed the radio from his 1987 BMW 325e and took the top off looking to unjam his cassette deck. Now he has re-installed the radio and has tried to punch in the code to re-activate it - but it won't come on.
He has tried to re-set by turning the radio off, turning the key to accessory, waiting an hour, turning the radio on and punching the code in - that didn't work. Then he tried to re-set by turning the key on, turning the radio on and leaving both on for 2 hours, then punching in the code - that didn't work. What is the exact procedure and what is preventing it from coming back on? Did opening the top of the radio activate something that stops the radio from re-setting? If it won't come on do we take it to a radio man or back to BMW? The 87 325is I just bought myself has a cassette deck that just ejects anything I put in it, so I'm needing to take another radio out but don't want the same problem as my father! Help! Thanks!

i sound like you tried it all i would go to bavauto.com and they can tell you what to do