The Apple A1407 Thunderbolt display may not work right away on some Dell computers. If your Dell computer's BIOS (or UEFI) has the following setting, please make the following change:
Use the appropriate key during bootup to enter the computer's BIOS.
Locate the setting "Thunderbolt Auto Switch" and uncheck "Auto Switch."
Select "BIOS Assist Enumeration."
Click Apply.
Save changes before exiting the BIOS.
Note: This setting may not be available on all Dell systems.