Hi there,
did you make sure to keep the video drivers within the image while syspreping? If not, the drivers will be removed.
Using the setup.exe with the appropriate command line switches should work perfectly. Extract the downloaded file from Dell and check the Readme.txt for the silent switch.
Also make sure that you understand and implement the HII correctly following the links on this site: OS Deployment and Provisioning. There are several docs referring to HII.
Good luck!