If you can still boot into Windows and just want to get to Safe Mode for some reason (eg., diagnostics) a simpler method may be to just do so from the PC Settings. Here's how:
|Windows 8 PC Settings|
- Press Win+C to bring up the Charms Bar.
- Click on Settings, then Change PC Settings.
- Head over to General on the left hand pane, then scroll the resulting right hand pane all the way down.
- Press Restart Now and Windows will reboot into the new menu that replaces the old boot time F8 menu. You'll need to navigate through this to get to Safe Mode.
- Choose Troubleshoot.
- Choose Advanced Options.
- Choose Startup Settings, and click on restart.
- From the new list that will appear press 4 to boot into Safe Mode.