Boot Into Safe Mode In Windows 8

                              In Windows 8, the boot has become so fast that it literally cannot be interrupted by any of your key presses.

• Open command prompt as administrator.
• Then type the following code in command prompt and press enter.

bcdedit /set {default} bootmenupolicy legacy

• If you typed the above command correctly then Windows will show you a new window saying "The operation completed successfully".
• Restart your computer.
• Then press F8 key and you can boot in safe mode without any problem.