As it is installed by default, Windows 8 does not allow users to install unsigned drivers.  This means that the ReplicatorG installer can't automatically install the drivers for you, and you'll need to make some configuration changes to be able use ReplicatorG.

The steps to install the Arduino & Makerbot unsigned drivers on computers running Windows 8 is as follows:

1. Uninstall ReplicatorG (if you already have it installed)
2. From Windows 8 Start or Desktop screen (either one), move the mouse cursor to the right side top or bottom corner to get a pop-out menu.
3. Select the magnifying glass icon (search tool)
4. Select the “settings” icon (the gear icon that is the second icon down on the right side)
5. In the search bar (above the icons) type “Advanced Startup”
6. On the left side of the screen you will see an “Advanced Startup options” box; click on this box
7. You will default to the “General” on the left side window; scroll the right side window down to “Restart now” 
8. Now the system will restart and might take some minutes to show up the boot menu. Wait for It patiently
9. After some time you will be prompted with a menu with following options.
a. Continue
b. Troubleshoot
c. Turn off

Choose “Troubleshoot”

10. Then the following menu appears.
a. Refresh your PC
b. Reset your PC
c. Advanced Options

Choose “Advanced Options”

11. Then the following menu appears
a. System Restore
b. System Image Recovery
c. Automatic Repair
d. Command Prompt
e. Windows Startup settings

               Choose “Windows Startup Settings”; then Click “Restart”.

12. Now the computer will restart and the boot menu appears.
13. Choose “Disable Driver signature Enforcement” from the menu (type the number “7”
14. Now windows will start
15. Install ReplicatorG; accept any prompt to install unsigned drivers (it may pop-up 3 or 4 times)
16. Run ReplicatorG, scan for serial port, and select your port
17. Ready to connect and print