Dear Chino de Oro, Problem solved. B.........R straightened out their issue and all ports work again. Thanks for your help.
As of yesterday, all USB drives do not acknowledge in MS Explorer when a USB stick gets inserted. Both the A. B and C ports, both in the front and in the back. Dell support checked everything, updated all drivers, etc. BIOS is latest release. All MS software is up-to-date. The ports work once, after a restart. But after removal of the drive the ports work no longer., until the next restart.
XPS 8930, all USB drives stopped working