Garage Door Opener Repair

What I have:
Genie Pro 98
1/2 hp, screw drive
single wide door
professional installed by previous owner
door does not have electronic eyes as a safety measure to reverse the door
house was built in 1973 but the open does not look that old, maybe 10 years old.

Here is my situation.
From the closed position, the door opens fine by pushing the doorbell like button mounted to the wall.
Once opened, pushing the same wall mounted doorbell turns on the light but the motor does not activate and the door does not lower.
I have been manually pulling the drive release cord to close the door then reengaging the drive cord as a way to lock to door from inside.

What seems to be the problem?
I know little about door openers.

Does the light blink when you try to close it? Every opener from the last I would guess 15+ years has had to have the electric eyes, it's possible that the PO just wired around them and that hack is no longer working?

I had a similar problem. check the wiring on both switches along the track. mine near the front of the garage had a loose wire.

After I posted here, i went internet searching.
I found this posting on what may be a common problem.
http://www.homebuyerstalk.com/showthread.php?s=e0a82e8346beb90f8baa69ffc54c085b&t=40275&page=2

Seems that the electric motor may "flat spot" over the years. The door goes up the exact amount and down the exact amount. The advise was to turn the main screw a quarter turn to manually slightly lower the door and thereby change the resting point of the motor off the "flat spot."

I did and the door has now successfully opened and closed 5 times.
I will keep an eye on it.

GrTech, Before I posted here I looking at all exposed contacts and wires. Thanks.

Other internet searching dates the model from 1980-1992

I have a weird house. It was built in 1973 by local super rich guy as a summer home to compliment his California winter home. He kept it 10 years and then sold it to another guy who also used it as a summer home until his wife died and he remained here exclusively.
We are the first people to put a full time use on things and though the house is nearly 40 years old, it has never really seen 40 years of use.
The kitchen was remodeled in 1994 in all white. She cooked very little and once she passed he never cooked again. It really looks tremendous for its age.

Canoe above but the garage door is still acting up.