To see if the transmitter or its battery are bad, check opener with the push button inside the garage. If it works, try replacing the transmitter's battery. If the transmitter still dosen't work, it's button may be defective or it may be out of sync with the receiver. Check your owners manual for help if it is off freq. If defective you may need to replace it. If you have a multifunction wall switch, make sure the security or vaction switch is not activated as this would prevent your transmitter from working. Conversely, if the transmitter works but the push button inside the garage doesn't, turn off the power and try electrical contact cleaner on the push button. If that doesn't fix it, turn off all the power and replace the switch. If your opener has electric eyes at the base of the track, check to see if these sensors are aligned (facing each other) and are not blocked by some object. There must be no obstruction between the sensors for the door to operate.