Galaxy S4 cannot connect to PC via USB.

Galaxy S4 won't connect as removable disk.

If you are using Android 4.3 or 4.4.2,  open dial pad and dial *#0808#
When menu open, choose : MTP + ADB, then press OK and then Reboot.
After reboot, connect phone to PC and after some moments, you have 
Galaxy's removable disk available.

Screenshot :