Safeguard doesn't load on reboot, does on power off/on

I have installed Safeguard on an HP Envy.  It works fine if you power the machine off/on, however if I reboot the machine from Windows it doesn't go into the safeguard bootloader, it just hangs on a black screen.  If I then power it off manually with the power button it comes on ok and into safeguard.

Ideas?

Thanks

Update - It doesn't actually appear to start safeguard at all, I don't even get the black screen with the white text or the ability to use the shift keys