Confused?

[Bilal8210]

Started the car this morning after driving around fine yesterday, started fine then i heard pretty harsh clicking sound then saw smoke coming out of the bonnet, after opening the bonnet found that part of the fan belt had ripped off itself, the belt was still fine though. after looking at it more closely found that the a/c belt underneath it was also goin very slow and it was that that was giving off the smoke and by then a very strong burning rubber smell. Dont seem to know how this happened while the car was parked in the same place overnight? other than this the car has been perfect over the last 1 and a half years ive had it. car has been booked into the garage and am replacing all four belts (fan, a/c, power steering and timing) to save me any bother in the future. any1 got any ideas on why this happened?