Software publishers have the ability to "sign" device drivers for hardware by embedding a bit of code that proves the publisher's identity. This helps you know that a device driver is authentic and safe to install. Because digital signing of device drivers enhances the safety of using a computer, Windows 7 won't install a device driver unless it's digitally signed. However, if you understand the risks and want to install a third-party or untested driver anyway, you can disable this feature from the Command Prompt.
Click the Windows orb and click "All Programs."
Click the "Accessories" folder.
Right-click the "Command Prompt" icon, and select "Run as Administrator." If you see a prompt titled "User Account Control," click "Continue." You now see a window titled "Administrator: Command Prompt."
Type "bcdedit.exe -set loadoptions DDISABLE_INTEGRITY_CHECKS" and press "Enter." Windows displays the message "The operation completed successfully."
Type "bcdedit.exe -set TESTSIGNING ON" and press "Enter." Windows confirms that the command is successful.
Open the Start menu. Click the arrow in the bottom-right corner of the menu and click "Restart." After the computer finishes restarting, Windows 7 will allow you to install an unsigned device driver.