i9505 connection problem

Hi all,
Sorry to be a pain on my 1st post, but banging my head against a brick wall despite reading countless threads.
Galaxy S4 locked to Three Network running 4.4.2
I have enabled dm modem adb, dm/dun over hsic,usb debugging,allow outside sources.
My computer now fails to recognise my phone other than unknown Samsung Android Modem.
I have tried reinstalling drivers & get the message the currently installed drivers are up to date.
When trying to unlock phone it just hangs searching for device.

Any ideas?