It’s a rather lengthy process to start Windows 8 in safe-mode for diagnostic troubleshooting.  I’ll show you the Windows way of starting in Safe Mode and then I’ll show you the quick way.

The Windows Way

1. Swipe in from the right edge of the screen, tap Settings, and then tap Change PC settings.
   (If you’re using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, click Settings, and then click Change PC settings.)
2. Under PC settings, tap or click General.
3. Under Advanced startup, tap or click Restart now.
4. On the Choose an option screen, tap or click Troubleshoot.
5. Tap or click Advanced Options.
6. Tap or click Startup Settings
7. Tap or click Restart.
8. On the Startup Settings screen, choose the startup setting you want.
9. Sign in to your PC with a user account that has administrator rights.
   

The Quick Way

Reboot system, hold Shift-F8.  Now *that* was easy.