Garage doors work with one of two different types of springs. Extension springs are at the back of the track on each side. Torsion (the sturdier of the two) are mounted directly above the door opening. We install torsion springs when we put a new door on, but service both types. If you cannot open your door after disconnecting the release, you may have a broken spring. (see below here)
Torsion springs installations are best left to the professionals. Because they are tightly wound, they can be tricky and dangerous to install.