j26 said:Plugging in a usb device wakes it up.
AlBDamned said:That link from WildCowboy also mentions Jiggler which does what you want for free.
gman71882 said:Plug in your DVI-VGA adapter that came with the computer. It doesnt have to go into anything.
The system will think there is an External Display hooked up and wont go to sleep when you shut it.