Welcome . Look at this thread. Maybe the tensioner pulley was not changed and needs to be changed? Or maybe the tensioner spring and bolt were left in place, came loose and broke the belt?
http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=zetecmaint&Number=672210&page=&view=&sb=5&o=&fpart=&vc=1

"Always do the cheap and easy ones first." 1996 V6 ATX 96K miles