Hi I eventually solved this problem.
My theory to why it happens:
When you turn on or reboot the SurfaceBook 2 it remembers what state it was in before you switched it of. You'll perhaps notice that your apps open as they were before you shut down. The glitch that causes the "won't turn on" problem is also resumed so the problem isn't cleared by a reboot.
What to try:
Make sure you have the latest Windows updates and at least 20% charge.
Hold down the power button, ignore the Slide to shut down your PC screen and keep holding the power button until the computer goes off and the windows logo comes back ... then release the button. If you get a prompt to do a disk check, just cancel it.
Once the computer is up and running you should find the problem has gone. I did this several months ago and I haven't had a problem since.
Hope it helps, let us know!
I tried this just now, and it seems to work so far. Mine was to the point that it would hardly ever wake up from one push, and now it's worked fine three times in a row.