I have the Craftsman 1/2 H.P. manufactured in 8/97 and it will not go up or down without reversing direction. I have tried cleaning and aligning the 'eyes' and the glow from both is solid green. When I use the wall switch, it goes for about 2 seconds then reverses direction. The light on the unit blinks 5 times then goes dark. I recently replaced the internal gears because the unit stopped working completely so I know it's not a gear problem. What can the problem be?

I assume you are talking about a Craftsman garage door opener.

Check the electronic lock button. Usually they will close but will not open if the lock button has been pressed.

I replaced the eye sensors and solved the problem