Hi!
We bought new Dell XPS 12-9Q33 with BIOS A3, Windows 8.
When we initially tried to do Factory Backup with Dell Backup and Recovery, utility didn't find USB drive no matter what trick we tried.
What finally helped was BIOS setting Advanced -> USB Emulation. It was set to Enabled and we changed it to Disabled. Backup utility was now able to find the USB drive.
I hope this will help somebody with the same problems.
- Mitja