I just bought a new Dell xps15z 2 weeks back. I have used it only 2-3 times and noticed whenever I shutdown the laptop after 2 seconds it turns back on. I havent installed or deleted anything from the laptop yet. I also noticed that the hibernate option does not work either. It is really frustrating to have issues with a brand new laptop. I am swamped with work too so unable to call Dell.. so i thought i would post it here and check if anybody else is having this issue?
I am sorry to hear that you are having problems with your new notebook. Just to make sure that there isn't some type of software causing the problem I suggest booting the system in Safemode and once fully booting into Windows click start and shutdown. See if the system shuts down correctly without rebooting.
If it does shut down correctly while in safemode then that implies that there is no problems with the Dell hardware, it is a software problem with the system. Make sure that all programs are closed before shutting down the system.
If you connect any external devices to the notebook disconnect them. Restart the system and once back into Windows click start and shutdown and see if there are any problems. If all of a sudden the notebook shuts down fine then it is likely one of the external devices that was causing the problem.