1
Are you able to force your Dell All-In-One PC into the Recovery Environment using there steps?
Start your PC, just as Windows attempts to load (spinning dots), press and hold Power Button for 5 - 10 seconds to perform a Hard Shut Down
Do this twice
On the third start Windows will boot into the Recovery Environment and from there you can access System Repair, Safe Mode, Command Prompt... etc.
2
If not, when you start your PC, what is the exact sequence you see on the screen, do you see the Dell logo screen, then do you see the spinning dots to indicate Windows is trying to boot up, and if so, at what point does that fail and what is the error you see on the screen.