I was driving the car, all of a sudden the battery light comes on and I loose power steering. I figuered the main belt must have snapped, i was only a mile from home so i made it. It was the main belt.

About three weeks ago, i replaced the thermostat, water pump and two drive belts. When replacing it, i accidently loosed the pulley and adjusting bolt above the tentioner. i though I tightened i put everything back in right, but three weeks later here I am.

Any suggestion where i may have screwed up with the install? or is there a proper way of tightening the pulley i loosened? or any other reason new belt would snap like that?