Two options:
1. Open the Command Prompt window by clicking the Start button, clicking All Programs, clicking Accessories, and then Right clicking Command Prompt and select
"Run as Administrator".
2. On the Command Prompt type in the command “Bcdedit.exe /set nointegritychecks ON” without the quotes.
This will disable the Digital Signature.
OR
Click start, and type gpedit.msc
ENABLE the option for code signed drivers at:
User Config/Admin Templ./System/Driver installation
then set the drop box to "Ignore"