To boot in safe mode Windows 8 follow the steps provided in this tutorial
Steps to boot in safe mode Windows 8
1.In your Metro Start Menu, move your mouse to the lower left corner and the Start menu pops up. Click on Search.
2. Type msconfig in the Search Apps text box and click msconfig icon on the left side.
3. Click on the Boot tab and then select Safe boot. Also click on the ‘Make all boot settings permanent’. Then click on the Apply button and OK. Now, next time when you restart your computer it will load safe mode automatically.
4. Alternatively, while restarting computer press F8 and you should see the following screen (window). Click on the ‘Use another operating system’.
5. Next, click on the Windows Developer Preview (Safe Mode). Now your computer will load in safe mode. That are the complete steps to restore Windows 8.
Safe mode is useful when your computer doesnt load in normal mode and you may want to disable some process.