USB Communication Failure
If a USB port doesn't see any connection, it means that your device doesn't pull the D+ wire up when it gets VBUS (or cable) in. You didn't provide any schematics of your USB connectivity (is VBUS sense used? is it self or bus powered), so it is hard to tell what is wrong. It could be wrong microcode that handles D+ connect signal, it could be miscalculated logic level on VBUS sense pin (if any), so the code doesn't start. Check with a scope if the device pulls up D+ (or D- if it is designed to be low-speed USB).