Windows 7 stuck in reboot loop following windows 10 upgrade

It's probably too corrupted to use. You need to repair it or reinstall.

The Vostro is stable at the moment, but I'm going to get my daugher to manually delete over 20gb of data so it's free enough to carry out a repair (too corrupted to network any files to another PC or Mac - I've started another thread on that).

The other fixed machine is working very well (given it's an old Dell Inspiron N5030).
Two things though:

1: Not sure if it's worth puchasing a faster Wi Fi dongle (interet is slower on that machine than this new Windows 10 machine).
2: There is a Windows message that appears periodically suggesting the registration key is incorrect. No idea what this is, but if close it down, nothing really happens, performance wise, with the machine.

I'll try and post a snapshot of it next time it appears.

Many thanks.