The Most Likely Causes
If the door feels impossibly heavy or won't budge even manually, a broken spring is the likely cause — springs carry most of the door's weight, and without one, neither you nor the opener can lift it safely. If the opener runs but the door doesn't move, check whether the trolley has disconnected from the arm (a red pull cord usually controls this) or whether a cable has snapped. A door that won't respond to the opener at all often points to a tripped or misaligned safety sensor, a dead remote battery, or a power issue at the outlet.
What to Check Before You Call
Look for a visible gap in the coil of the spring above the door, confirm the opener is plugged in and its light is on, and check that the two small sensor boxes near the floor on each side of the track are clean, aligned, and not blocked by anything. Telling us what you find speeds up diagnosis.
When This Is an Emergency
If your car is trapped inside or the door won't open and your home's security depends on it, treat this as urgent — see our Emergency Garage Door Repair page. We're available 24 hours for exactly this kind of situation.