Your serial number has two possible codes. In order of probability they are:
Your radio must display CODE to input the code. If it reads OFF, you must leave the key in the ignition key in the accessory position for one hour to resore CODE status.
To input the code, press preset button one repeatedly until it displays the correct first digit.
Press preset button two repeatedly to set the second digit, and so forth with preset 3 and 4.
Once displayed, press the unlock button for your vehicle. This button is always either CD, AM/FM, or TAPE, and varies by model. There is no penalty for the wrong button, provided the code is displayed correct. When the right unlock button is pressed, the radio will turn on.
Do the first code 2825 first... It is rare that there are more than one code for each serial number, but in my experience when this happens it is always the first one :)
If you have any questions or need more help, just ask.