In device manager, right click the phone, Update Driver, Browse my computer for driver software, Let me pick from a list of available drivers on my computer, and selected "MTP USB Device" There will be two, makes no difference which you choose
This was because of a bad driver update in Windows update. The update has been pulled but it effected most Windows 10 PC's.
It was the 'Microsoft WPD 5.2.5326.4762' WPD is windows portable device