Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Not enough power on the USB port to charge and run the display at the same time. Check the charge level, turn off display, charge it for 30 minutes or more then check charge level. It should have increased. Your PC USB port only allows 1 amp for power. The iPad prefers 2.1.
 
When i used to have to sync my iPad with my laptop for putting things on to it a few years ago i had to use a powered USB hub to do it, laptop USB didnt shove enough power out to connect properly let alone charge it.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.