I have a Chamberlain Whisper Drive and it started beeping. Reading the manual, it seemed that I needed to replace the battery. It is about 5 years old. Replaced the battery and the LED is no longer red but yellow and the door won't open. We did open the door manually a couple of times with success while waiting on the battery to arrive. What can we try now? Is there a reset button? We haven't seen it yet.

This is battery related. On top of your unit is a battery pack with three colored led lights. You can tell what is going on by looking at these. This information is in your manual or here it is.
GREEN LED: All systems are normal. A solid LED light indicates the batteries are fully charged. A flashing LED indicates the batteries are being charged. NOTE: Batteries do not have to be fully charged to operate the motor unit. YELLOW LED: The motor unit has lost power and is operating off of the BBU. A solid LED with beep, sounding approximately every 2 seconds, indicates the motor unit is activating the door and is operating off of the BBU. A flashing LED with beep, sounding every 30 seconds, indicates batteries are low. Once the power is restored the BBU will recharge. This is indicated by a flashing GREEN LED. RED LED: An error has been detected and the BBU will automatically shut off. The BBU will attempt to restart by reconnecting to the batteries. If the error is still present it will shut itself off again. This process will repeat every 5 minutes or until the error has been resolved. This is used to prevent further draining of the batteries. If a red LED remains on when the power is restored, and is accompanied by a beep sounding every 30 seconds, please call for service.

On the back of the garage door opener there is a red button. Depress this button and sync your keypad to the opener. This will re-establish the code and reset the remote.