If the radio nor the cassette work then I would suspect that your radio has NOT accepted the security code. First make sure you have the correct code ,...........(Post another question on here quoting MAKE, MODEL + SERIAL NUMBER of the radio to confirm the code if necessary )....... then disconnected the fuse or battery connector for 5 minutes, replace then enter the code. Make sure that the display + beeps denote that the code has been accepted.
Entry instructions are here
http://www.davidsonelectronics.co.uk/code_entry.htm
RegWorts, June 2008