I'm in the same boat.  My computer wont go to sleep and stay asleep, it restarts.  I've reloaded windows, I've tried running the boot USB and run the bios downgrade, but the system restarts and fails to downgrade the bios.  

Thanks

I was able to downgrade the bios to 1.5.1 following the instructions here.

http://www.dell.com/support/article/us/en/04/sln300716/bios-recovery-options-on-a-dell-pc-or-tablet?lang=en

I have a similar issue. I was on 1.5.1. updated to the faulty 1.6.1. I was able to rollback to 1.5.1, but if I do bios recovery and recover current bios it recovers to 1.6.1.

So I mounted the esp folder and there is BIOS_CUR.rcv which I assume is 1.6.1 in my case.

BIOS_PRE.rcv is 1.5.1, I know this because I renamed it BIOS_CUR.rcv and the did bios recovery to recover current bios (not previous) and now the bios number is 1.5.1

I am requesting somebody with successful 1.7.0 bios install can you sent us your BIOS_CUR.rcv and I can try reset to that bios?

Install minitool partition wizard, mount the esp partition with a drive letter and apply. Run notepad or notepad++ as admin. Then find use the open file dialogue as a file explorer, navigate to ://efi/dell/boot/bios and copy both .rcv files and put it into a folder in C (all while using the open file dialogue)

Maybe this method can be used to bypass unsupported downgrade as I'm hoping it blindly flashes the .rcv file

The symptoms I'm having is when running the bios update exe, it will reboot the machine, take about 15 seconds. The charging light comes on, then keyboard, then black screen. It immediately turns fully off with no lights. Then boots up a good 20 seconds later normally without reaching the bios update screen.

Sleep is messed up for me, and it takes 1 full minute to get to the windows loading screen as it takes forever just to boot past bios screen.

I figured out a way to do it. 

1. download the 1.7.0_bios.exe and rename it to BIOS_CUR.rcv
2. use the method above to access the efi boot folder you will see multiple .rcv files.
3. leave the BIOS_PRE file as is (will be a backup if things fail)
4. rename the existing BIOS_CUR.rcv  to OLD_BIOS_CUR.rcv
5. use notepad to copy the BIOS_CUR.rcv from the downloads folder to the efi folder with .rcv files
6. turn off your laptop and unplug the power
7. hold ctrl + escape while plugging in the power cable
8. choose to  recover bios
9. this will recover using the new 1.7.0 bios as it restores BIOS_CUR.rcv 
10. check the bios version it should be 1.7.0

i did notice that it doesnt fix the sleep issue. im trying to get it to hibernate when you close the laptop