Disable driver signature enforcement or Enable low-resolution video mode in Windows 8 Consumer Preview (Works with 64-bit)
Select Settings from the Charm bar (on the right) > More PC Settings (at the bottom)
Then go General > Advanced Startup > Restart Now
Then Troubleshoot > Advanced Options > Windows Startup Settings > Restart
As your PC is starting up keep hitting F8 to get to the menu where you
can choose to disable driver signature enforcement or Enable
low-resolution video mode or Enable safe mode.
or this:
Use these two commands from CMD(Admin):
bcdedit -set loadoptions DISABLE_INTEGRITY_CHECKS
bcdedit -set TESTSIGNING ON
To turn back on use:
bcdedit -set loadoptions ENABLE_INTEGRITY_CHECKS
bcdedit -set TESTSIGNING OFF
This way you won't have to disable every time PC is restarted.