Initially the update could have exacerbated an already existing problem, which you were not aware of. Perhaps with each restart Windows repaired itself a little until enough was fixed to finally boot-up.
Try running Dell's Diagnostics:
https://www.dell.com/support/home/en-nz/...
Personally I would do the full test which takes 40 minutes.
Let us know how it goes and report any errors it finds.
Updating drivers would be a good idea. Is your BIOS version A07? You can check from the BIOS screen.
Entering System Setup (BIOS)
NOTE: Before entering the System Setup, you must connect a USB Keyboard to the USB port located on the right side of the computer or on the rear of the docking station if your computer is docked.
1. Turn on (or restart) your computer.
2. When the blue DELL logo is displayed, you must watch for the F2 prompt to appear.
3. Once the F2 prompt appears, press <F2> immediately.
NOTE: The F2 prompt indicates that the keyboard has initialized. This prompt can appear very quickly, so you must watch for it to display, and then press <F2> . If you press <F2> before you are prompted, this keystroke will be lost.
4. The System Setup screen is displayed.
5. If you wait too long and the operating system logo appears, continue to wait until you see the Microsoft Windows
desktop. Then, shut down your computer and try again.
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