Trolley Rail Jam

Hi, my power was out last week and had to open my garage door so I unlocked the trolley from the rail and opened the door. The next day the power went on and I had forgotten to engage the trolley on the rail and the lock square when the trolley locks in place ran to the end of the rail and it now stuck. When I try and use the remote control nothing happens, but I can hear the motor straining so I stop. What can I do to correct this? The chain is extremely loose, while the cable wire on the opposite side of the rail is very tight. Any help is appreciated. Thanks.

Note: Opener is a Chamberlain 1/2 H.P. Security Plus

Sometimes by loosening the chain and then trying to operate it will free it up. But before running it back down, be sure to adjust the down limit so it doesn't happen again and also tighten the chain back up.