Sounds like a bad logic board to me. I would most likely opt for a new opener.

Try a few things first. Disconnect the wires from both sensors. now power cycle the opener. the main light should blink on and off. On some openers it will stay on for five minutes or so. Now try to make the door open by simply pressing on the wall button. It should open. Now try to close the door by putting constant pressure on the wall button. Door should close. If you fail any of these tests you have a bad board.

If this works then connect the sending unit of the beams. If the sending unit has a light it should light on solid. Check wires if it does not. Now connect the receiving unit. It should also light up solid (after aligment). If the receiving unit keeps blinking then the problem is the sending unit not sending the IR beam.

If you decide to purchase a new opener see about an idrive from Wayne-Dalton. It does not need to use the beams.