1. Look in your glove box for a white sticker with black numbers on it. The sticker will be about 1 1/2 inches long and 1/2 inch wide. There should be 5 digits on it. These 5 wonderful numbers are your radio code. Put the code in through the preset buttons on the radio. You'll hear a beep and the radio will come back to life. (though you'll have to reprogram all your presets)
2. Ok, there's a sticker there, but there's more than 5 numbers on it! What do I do with that? Don't worry, that's the serial number for the audio unit. Call a dealer, tell them what happened and that you have the serial number and they can get the code for you for free. Write the code down and stick it in the glove box. Follow the steps in #1 above.
3. There's no sticker in my glove box, what now smart guy? Don't panic if you don't find a sticker, there are other places it's put sometimes. Check your sunglass holder (applicable models), the center console, even under the arm rest. I've even seen them under the cover of the under-hood fuse box. Check all these places before panicking.
4. Ok, I've checked everywhere, and there's no sticker to be found! Still not time to worry, try this: get a pen or pencil and something to write on, place them in the car somewhere handy. Turn the radio OFF.Turn the ignition to on, but don't crank the car. (You'll need to free hands for the next step). With one hand, hold down the 1 and 6 on the preset buttons, with the other, push the power button for the audio unit. You should see a letter and 4 numbers, wait a second and you'll see another letter and 4 numbers. Write these down. Don't worry, they'll scroll past twice. This is your serial number. Call a Honda
dealer and give them the number, they'll give you the radio code. Put the code in as in step 1.
5. Ok, Mr. Smarty-pants, I've done everything you said and still nada! On some models, the trick in step 4 will not work. If you've checked everywhere conceivable for that sticker (including the paperwork that came with the car...you do still have that, right?) and still can't find anything, you may have to call the dealer. They WILL have to pull the radio out of the dash (a process of at least 30 minutes) and they will charge you for it.
Hopefully, these were helpful tips, and you now have an operational audio unit.