Windows unresponsive and unfixable

This is a strange one - something seems to have become corrupted in my virtual machine and I'm really struggling to figure it out. I'm running insider build 16251 which has been running fine for a while.

What happens is I log in but am unable to launch any modern applications. At some point the screen flashes and it looks like Windows goes into tablet mode but at this point the start bar becomes unresponsive, I can't open the start menu and in task manager the CPU runs at 99-100%. Sometimes nothing is listed as using CPU, sometimes its system interrupts. Sending Ctrl-Alt-Delete does nothing and I can't restart the machine only 'Reset' it.

I've tried using a recovery drive but there is no option to reset the machine and when I try and reinstall Windows it tells me the target drive is too small. Any suggestions?