Sounds like your logic board might be going on the fritz. If you think you might want to replace it yourself, I can tell you where NOT to buy it. I recently bought one from Ontario Supply in New York from their web site for $60. Unfortunately, it has turned out to be defective and they won't refund my purchase price even though I sent the defective unit back at my own cost. So, don't buy from them, they don't deal fairly in my opinion. I think you're best off just calling a local repair service and let them replace the board. If you replace the board yourself and it does not work, you're just going to end up calling a repair service anyway. Ontario Supply operates under the following web sites:

http://www.wholesalegaragedoorparts.com

and

http://www.liftmasterpartsonline.com/

In my opinion, you should avoid this company

It sounds like you have a broken door spring or maybe a stripped drive gear. The gear is white nylon and is just in front of the motor. The spring should be obvious.