So, I had a go at dual booting android and windows 8.1.
It borked the boot system and I couldn't run either OS - so I eventually got it to reset to win 8.1, but not without a small annoyance.
Every time I switch on the tablet I get a dual boot menu:
Unetbootin doesn't work, but 8.1 is fine.
How do I remove the boot menu and get rid of unetbootin? It used to be a case of editing BootIO or IO.sys in the root directory, but they aren't there any more.