Data Execution Prevention (DEP) is a security feature that can help prevent damage to your computer from viruses and other security threats. Harmful programs can try to attack Windows by attempting to run (also known as execute) code from system memory locations reserved for Windows and other authorized programs. These types of attacks can harm your programs and files. DEP can help protect your computer by monitoring your programs to make sure that they use system memory safely. If DEP notices a Program on your computer using memory incorrectly, it closes the program and notifies you. It is as such a security feature.
Type cmd in Vista's search bar. Rt click on search results 'cmd' and click on Run as Administrator. Then copy paste
bcdedit.exe /set {current} nx AlwaysOff
and hit enter. Reboot.
To enable back DEP, type instead:
bcdedit.exe /set {current} nx AlwaysOn
Thats it !