Dell XPS Consumer Information page 23

Dell XPS Notebook Reimage "How-To" Guide
2. If OS setup in AHCI mode, need to confirm the setting is not changed to RAID or load to BIOS default
a. If the mode is different from the original setting while OS installation, will meet the problem that system
can't boot to OS with BSOD(Blue Screen of Death)- INACCESSIBLE BOOT DEVICE.
This can be resolved after going to BIOS setup menu and change the mode back.
b. Fail symptom for the wrong SATA mode