DIAGNOSIS That three-beep pattern is the opener telling you the safety sensors aren't seeing each other. The beam is blocked or misaligned.
FIX First, check the little LED lights on each sensor (they're down by the floor on either side of the door). 1) The one on the sending side should have a solid green light. 2) The one on the receiving side should also have a solid green light. If it's blinking or off, the beam is broken. Look for cobwebs, dirt, or something physically blocking the lenses. Gently wipe them clean. If it's still out, loosen the wing nut on the bracket and tweak the sensor until the receiving light goes solid green, then tighten it back up.
IF THAT DIDN'T WORK The wire running from the opener to the sensors might have a break or a bad connection. Trace the thin white wire from the back of the opener head unit down to the sensors. Check for any pinches, cuts, or where the wire might have pulled out of the terminal screws on the back of the opener. Tighten those screws.
HEADS UP Don't bypass the sensors to make it work—that's a major safety hazard. The door won't close without that beam as a failsafe to prevent it from coming down on a kid, pet, or your car bumper.