When you enable fast startup, does the system shut down fine? Does it restart / hibernates fine? Does it resume from auto / manual sleep fine? Does this happen with or without the adapter connected?
Restart and check in safe mode - http://bit.ly/1lJHAvx
Uninstall the video drivers from device manager and try shutdown. If it works, the video driver might be causing the issue. Reinstall the driver from the vendor site - Intel.com / Nvidia.com
Enable the built in admin account and check - http://bit.ly/IL7qlV
Also, please click my DELL-username and write me a private conversation with the service tag and your contact details(Name and Email) for case records.
Let us know if you have any other queries.