Solved! Go to Solution.
You have to press the power button until it clicks down, and continue holding it. After many seconds - at least 10 or more - you will hear the system shut down. Fans will stop, hard drives will stop, and the laptop is now off. Let it set for a minute to cool if needed. When you boot it back up it may automatically go into a repair/diagnostic routine. If not simply run the diagnostics from Dell's support website. Or alternatively run them from the support assist program.