itunes sync grey

Over the past few weeks i've not been able to sync my iphone 6 to my PC.

The sync button is greyed out and the storage bar at the bottom is just yellow with "other"

I've tried every fix i could find. I know it's this pc as 2 iphones won't sync on this pc but sync fine on another laptop.

Rebooting both pc and phone.

Updating drivers

updating itunes and phone

Uninstalling anti virus and allowing in firewall/turning firewall off

clearing lockdown folder so it can trust the pc again

authorising the pc.

The only thing i've not done is reset my phone for fear i won't be able to sync and i have no backup......

Any ideas guys?