How to Disable Driver Signature Enforcement in Windows 8

Move your mouse cursor to the upper right part on the screen
then select Settings ->Change PC Settings->General -> "Advanced Startup" -> Restart now.

The system will restart and might take some minutes to show up the boot menu. Wait for it patiently.

After some time you will be prompted with a menu with following options:

Choose Troubleshoot.

The following menu appears:

Refresh your PC
Reset your PC
Advanced Options

Choose Advanced Options.

The following menu appears:

System Restore
System Image Recovery
Automatic Repair
Command Prompt
Windows Startup settings

Choose Windows Startup Settings, then Click Restart.

The computer will restart and the boot menu appears.

Choose "Disable Driver Signature Enforcement" from the menu.

Windows will start and you can complete the installation of the driver that is not signed.