Please take a look at the DK2 Setup Guide in the vorpX help. It explains two possible ways to get the games to the Rift. Make sure to follow all steps mentioned there.
Here’s the short version. Please still read the guides in the help, they all contain important information.
You have two options to use vorpX:
A. The convenient one (works with most games)
1. Set the Rift DK2 to “Extend Desktop to HMD”
2. Use the Rift DK2 as SECONDARY monitor in Windows
3. Set the Rift DK2 to “Portrait” mode in Windows
(might be “Landscape flipped” in Windows 8)
4. Set vorpX to “Show on DK2″ display wise in the vorpX config app.
B. The compatible one
1. Set the Rift DK2 to “Extend Desktop to HMD”
2. Use the Rift DK2 as PRIMARY monitor in Windows
3. Set the Rift DK2 to “Portrait” mode in Windows
(might be “Landscape flipped” in Windows 8)
4. Set vorpX to “Use system settings” display wise in the vorpX config app.