iPhone 5S crashed

I Was charging my phone through my work PC and was finding it to be slow, so I reset it.

WHen it started up again it had no service.

I Took it to the iStore and they said it had a possible hardware problem.

I Then handed it in at my service provider for repair.

THey said it can not be repaired.

I Tried other channels to have it repaired, same story.

I Suspect it could only be a virus from the PC.

WHen it starts now it says iTunes and shows I should insert my cable.

PLease help