After cable replacement, Craftsman garage door won’t “close”, moves a few inches down, then back to further than it started

I have a Craftsman automatic garage door that came with the house. A few days ago, my wife informed me that the garage door was "making funny noises". Since we'd just gotten home late at night, and she mentioned it after we'd headed off to bed, I figured I'd check it out in the morning. Well, the next morning, she got into the car, hit the button, and the cable snapped. It had worked its way off of the pulley and had frayed and finally snapped (this had probably been going on for some time, explaining the noise). I disengaged the safety latch to raise and lower the door manually until I could get a replacement cable.

Well, I got the cable and installed it, but it's still not working. When I push the button, the trolley moves forward about three inches, stops, then moves backwards to the restraining bolt and stops. Right now, the cable is not connected to the door itself, as it's got the trolley too far back to connect. I loosened the chain using the bolts and we tried it again. It again moved the trolley forward a few inches, then just kept pulling it back until it was at the farthest position. The chain from the trolley to the sprocket is taut and the trolley is pulled back too far to hook into the door (normally, it would do so when it moved down to the door, but it's not getting that far).

Things which I've considered:

• The sensors – I cleaned them off and verified that they're lighting up fine. I also tried raising the door manually as far as it could go to verify that the lowered door wasn't somehow tripping them.
• The chain – I considered the possibility that I messed something up when putting the chain back on (it had fallen off of the sprocket after the cable snapped. But I think that this is simply the position that it wound up in after attempting to reel in the cable after it snapped, there in the upper position.
• The cable – I checked to be sure the cable wasn't catching on Anything. It is a little bit long at this point, but that end of the cable goes towards the motor anyhow, and it's not catching on anything.

I'm pretty close to just calling a repair guy, but I figured to see if I'm missing anything obvious. This garage door was working before the cable snapped and I tried replacing it.