Anyone give me an idea on this ?

I changed the water pump the other day on Lindsay's 1400 cc zetec se engined fiesta ! Went for a drive after all ok and it was fine the day after! Day after that she was doing a slow manoeuvre and had full lock on and says she heard a slight bang and its been miss firing and cutting out since ! I thought I bet alternator belt has snapped as I struggled with tension on it but when I got home and looked it hadn't ! Can't see anything obvious and know nothing about them!!! Sounds noisier too more tappety!