The original radio code is required and this can be retreived from the serial number, for a Blaupunkt radio this number will start with 'BP' send it to this link and pay a small fee: Car radio codes in Uxbridge London Gumtree
almost all this radios are protected in case of robbery stealing thats why they block suddenly
and the only way to disable the code is in any chevy dealers they have the master code only if youre the owner
if you push eject you should ear the little noise motor running
but yo dont have any disc out
they are stuck so you have to take it nearest repair shop