Just in case the door is just doing a "sticky" thing...
Climb up and pop the cover off the automatic garage door opener... there is a screw /knob thingy in there that adjusts tension and balance that occasionally needs a little twist this-way-or-that to correct the problem.
I found this out from a garage door repairman who said this is quite typical due to 'settling' (or in our case, bombs that shake houses). He fixed the problem in about 30 seconds flat (and charged me $80).
I'd spent weeks fiddling around with the chains, tracks, and spring and it turned out to be a super-easy DIY had I but known.
If that doesn't solve the problem, post back and I'll go dig up the guys phone #.