I had a little trouble back there Installing the fastboot drivers with Windows 8 x64 system.
It looks like Windows 8 Only Installs the driver after verification on signature check.
I solved the problem after much reading... thought a guide would help others.
In case if you are facing the same problem, follow the steps below.
The steps to install a unsigned driver on windows 8 is as follows.
1. From windows 8 control panel choose General –> Under “Advanced Startup” –> Restart now.
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.
3. Turn off
Then the following menu appears.
Refresh your PC
Reset your PC
Choose Advanced Options
Then the following menu appears
System Image Recovery
Windows Startup settings
Choose Windows Startup Settings, then Click Restart.
Now the computer will restart and the boot menu appears.
Choose “Disable Driver signature Enforcement” from the menu.
Now windows will start and you can do the installation of the driver that is not signed.