I removed the head unit, put it back in exactly as it was, and now the radio/clock won't turn on. However, the car works perfectly fine, the theftlock on the head unit flashes, and the backlight comes on at night, just no radio/music.

Any ideas on what might have happened? Any fixes?

Probably have to punch in theft security code. If you have never picked your own, factory default is 0000, at least that'* what I had to do.

GM DELCO THEFTLOCK RADIO UNLOCK CODE:
1. Press and hold presets 2 and 3 for about 5 to 10 seconds until you
get 3 digits on your display. This is the first 3 of 6 digits you will
need, so write 'em down.
2. After doing step one and writing down the code, immediately press
the
AM/FM button to get the last 3 of the 6 numbers you'll need, and write
'em down. (if you wait too long between steps 1 and 2 and the LOC code
displays again, just start over).
3. Call this number, it'* a prerecorded message, so don't worry about
having to talk to anyone...1-800-537-5140. The voice will ask if
you're
calling for Chevy, Pontiac, Cadillac, etc... When you here him tell
you
to press "2" for Pontiac, press 206010 and hit the # key. He'll ask
you
for the 6 digit code that you've written down. Enter that and press
the
* key. He will then give you a code, and the option to get additional
4
digit codes, but one should be sufficient.
4. Follow the normal procedure in your owners manual for unlocking the
radio with your new code...press the hour set button on your radio
until
you get the first two numbers of the code, then press the minute set
button until you've entered the last two numbers. Immediately press
the
AM/FM button once the correct code is entered and the code SEC or
"secured" will be displayed on the display screen. Now, just turn the
radio on, and your ready to roll.
There is an additional step you can take to remove all codes from the
radio and start from scratch by entering your own personalized 4 digit
code so that it won't get you in a pickle again! Just repeat step 4
and
you should get a display screen that reads ---. This means the code is
out, and you can now program your own code. Of course, once you
receive
the 4 digit code from the GM recorded message, just keep it in a safe
place, because you can use that same code again and again should you
have any more problems with it in the future. Good luck, and yes, it
does work.

Sorry if my initial description wasn't clear enough, I should have emphasized there is nothing on the screen, but the backlights and the theftlock light still show up.

I know exactly what you're talking about with the security reset. However, the problem is different in that the radio doesn't turn on at all. The screen is completely blank (it doesn't say "LOC"). Any guesses on what this could mean? Everything was put back how it was before.

Ohhh ok, sorry I misunderstood you.
I'll see if I can dig up any information on that issue, right off I am unsure because I have not encountered that issue before.
Have you double checked the radio fuses, if so maybe you will need to remove the unit again, and examine the connectors, make sure no wires have came out of the adapter.


I searched for a while and all I can find is the info for when it says LOC.
The only thing close to relevant that I could find is for a Delco radio on a tractor, I doubt it will help you in your case, but I'll post it just in case.



The following procedure is the process to turn the Theftlock LED OFF:

1) With IGN ON and Radio turned OFF, press and hold the DSPL/TM set button until the HOURS digit flashes.

2) Press and release the Preset "1" button. The display will say FLASH ON to indicate its current state.

3) Press and release Preset "1" button until display says FLASH OFF.

4) After about 5 seconds, the display will return to time of day.

5) Check for desired operation of the Theftlock LED.

6) Reverse the procedure above (steps 1 - 5) if it is preferred to have the Theftlock light flashing

So what you are saying is, you have no display? Does the radio head light up when you turn your lights on, and change with the dimmer switch?

Have you tried to turn the radio on, even without a display? Do you have sound with no display?

Recheck your harness connection for power and ground.....recheck your antenna connection....

either you blew a fuse or one of the plugs got a loose wire. one time i took the radio out of my bonnie and the one was so tight before you could access the plug it was rubbing the insulation off. you could have done that and blew a fuse if it was the power wire

I'll answer your questions in order to the best of my knowledge.
Correct, there is no display at all. The backlights for all of the buttons are still affected by the dimmer switch.

I've tried everything I can think of to try to turn the radio on and it has no power, no display, no sound.

I'll make sure to recheck those and I'll post if those have done anything.

Pay special attention to the antennae being hooked up, it can act as a ground, also pay special attention to any red, or yellow wires of the radios wiring harness.
Also double check fuses.

I never did like the way those double DIN radios slid into its holding tray. Sometimes the radio harness gets pinched on the metal slider. Pull the radio back out and verify voltage at the yellow and orange/red wires.