I've run into a following problem with Win 10 installation.

A month ago I've bought an inexpensive Atom 3735F + 1 GB RAM + 16GM storage Win 8.1 tablet.

I've first tried to install Win10 using "forced" windows update option (wuauclt.exe /updatenow), but it didn't work - probably because of not enough free storage space.
Then I've created a bootable USB pendrive with Win10, but the setup would quit. Now I know why - the pendrive was broken.
So I've decided to perform a clean Windows 10 installation by booting from the pendrive.
And here are several mistakes I've done: I didn't write down the Win 8.1 key before removing Win 8.1 partitions. I forgot that I would have to do the upgrade first for Win 10 to activate properly.

So here is where I am now:
I've performed a clean Win10 installation, by removing all the Win 8.1 partitions and I don't know what my Win 8.1 serial key is.

Now, the problem with Win10 is that it is stuck in some sort of a boot loop: Windows boots, asks me to choose a WIFI/3G network and choose the settings (express etc.), then it loads for few seconds (spinning circles), then it reboots and I'm back again asked to choose wifi/specify settings...

I want to be at least able to use my tablet before I get the Win 8.1 key from the manufacturer (I hope it is possible) and do the upgrade procedure correctly.

Any ideas on how I can quit this boot loop? Do you think the manufacturer might make any problems with providing me my original Win 8.1 key?