Diagnosis
The opener has lost its programming and is in a standby state. The solid green light indicates it has power but no programmed travel limits.
How to Fix It
You must reset and reprogram the travel limits. Pull the red emergency release cord. Manually move the door to about halfway open. Plug the opener back in. The light should flash amber. Press and hold the 'Learn' button for 6 seconds until solid amber. Then press and hold your wall button to set the open limit. Close the door manually and press/hold the wall button again to set the close limit. Reconnect the door.
If That Didn't Work
If the light stays solid green and pressing the 'Learn' button does nothing, the logic board may be locked up. Unplug the opener for 5 full minutes to perform a hard reset, then try again.
Heads Up
Do not try to run the door before setting limits. It could drive the trolley into the end of the rail and cause damage.