[H23A1Lude]

The 5 digit code SHOULD BE on a sticker found on the side of the glove compartment. Usually on the outside left when you open it up. There are two numbers there - you want the five digit one. Once ten attempts are made without the correct code being entered the system locks itself up and will not accept any code. This is to keep someone crazy enough to keep trying random numbers, such as a thief, from eventually finding the right sequence.
There are two ways of releasing the block. The first is to run the radio for an hour. No sound will come out but once it has been on for an hour it will unlock itself and you can put in the code. Or, disconnect the negative battery cable for about a minute and then reconnect. You now can enter the code and all will be well. Well, except for the fact that now you have to reset your clock as well but if you will go through that much to get the radio back setting the clock is probably withing your area of expertise.
Let me know if this helps.