We bought a Dell OptiPlex 5250 with the latest chipset (Core i5 Gen. 7) lately. I started to create a bootable USB stick with DIA but after booting from this stick(with UEFI, but also with legacy) it says:

Initializing Dell PE, this may take a minute...

Waiting for USB Drive to be ready...

Unable to locate USB Drive.

X:\windows\system32>

 

I found no way to boot from the DIA-USB stick, neither it is located in the 3.0 nor the 2.0 USB ports.

Any suggestions, what I did wrong?