PVC replacement gone bad ??

I bought my car to a new service station for an oil change
a month later I was driving heard a whistling noise and
engine light came on. I bought it in to dealership for repair.
They said it was a cracked pvc and replaced it.( Covered
under warranty).  They recommended new spark plugs
and some fluid flushes which I did not get. Car drove well
for 1 day. Next day went to turn car on radio came on but
car did not turn over. Dealership has had my car for a
week now and not finished. Any ideas what this could be