Hey, go to the BIOS Setting, then Display and disable the "Hybrid Graphics". After your Deployment you can enable it back. It's just an workaround, but for me it helped to install every Precision 7670 Devices which I have here. 
Hello We've been imaging Dell PCs for a while now so we've had the process down. We recently got the Precision 7770 and the PC can't seem to launch lite touch after the files have been transferred. We get this result whether we launch it through windows or PXE boot. The Dell logo displays and it just hangs. Has anyone else had this issue and what did they do to resolve it? We made sure that the BIOS was updated. Disabled secure boot Tried a Dell USB C to ethernet adapter    
Precision 7770 hanging after lite touch download on MDT