Since I spent several hours troubleshooting my garage door (Sears Craftsman 1/2 HP, 1997 model) remote controls, I thought I'd post the following FYI;

Resetting the passwords and remotes
1. Hold the square red button on the garage door opener unit for over 6 seconds.

Setting up a remote or both remotes
1. Press and hold any button on the remote, preferably the big button (pick which one you want to use, any of the three can be used).
2. Press the square red button on the back side of the garage door opener unit.
3. The garage door opener light should blink and you're all set.

If a remote does not blink the orange light when holding any button, then either:
1. Change the battery and retest - or -
2. The remote is bad.

You should have two remotes and it's likely that one will work and you can use its battery to test on the remote that may be bad.

If you have a new car with built in remote controls, then you can program your remotes using the "Setting up a remote or both remotes" section. The only thing you'll need are really long arms or two people. One person has to hold the remote button (in your car) and one person then has to push the red square button.

Setting up the outdoor remote (mounted on a wall usually)
1. Press the square red button on the back side of the garage door opener unit.
2. Go out and and input the new PIN on the wall mounted remote keypad and press enter.
You have 30 seconds to go outside and set the new PIN.

I'm not sure why these remotes go bad since they look incredibly simple. I'm not throwing my bad remote out just in case one day I can fix it. They're pretty pricey (+$30). Good luck, hopefully you'll save some time.