LADY WHO DOESNT KNOW CARS WANTS 2KNOW WHY BELT IS LOOSE AGAIN MNTHS AFTR REPLACD

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BELT AND WATER PUMP RECENTLY REPLACED. CAR RAN OK. NOW BELT IS LOOSE AGAIN. CAR SUDDENLY LOST ABILITY TO MOVE FLUENTLY. HAD CAR JUMPED. AAA SAID ALTERNATOR SHOWS PROBLEM. AFTER JUMP WITHIN 20 MINS IT WOULD DIE. HOW ARE ALL THESE PROBLEMS INTERCONNECTED> WHAT ORDER OF THINGS SHOULD I CHECK FIRST, SECOND. WHAT COSTS AM I LOOKING AT PARTS/LABOR NEW/USED PARTS. I COULD USE AS MUCH INFO AS POSSIBLE AND ASAPPPPP ANYONE WHO KNOWS CARS PLEASE HELP! MUCH APPRECIATED.