There are several things that might cause this.
Check the Basics
1. Make sure your system meets the minimum requirements listed here.
2. Make sure you are running the most recent video and audio drivers available for your hardware.
3. If your game is launching but crashing or freezing in the middle, please see this article instead.
4. If you are using Windows 8, there is a permissions issue that will prevent you from launching our game client. We have a temporary workaround here while we get this fixed!
Adjust Your Permissions
1. Disable your firewall software. (This includes internet security suites). This lets the game properly communicate with our servers. Details on this are located here.
2. Make sure you are running Orcs Must Die! Unchained as Administrator. Additionally, if you are using Steam, make sure Steam is being run as Administrator.
Improve System Reliability
1. An unstable connection can cause the game or the training to stop running. Using a wired connection instead of a wifi connection can help with this.
2. Third-party programs can cause trouble here, too. Virtual Audio Cable, Nvidia Shadowplay and Nvidia Optimus have caused issues, for example.
3. Additional devices have shown issues as well. USB docking stations and Digital-to-Analog Converters have shown to cause this issue.
4. The transition from the dashboard to and from the game client is very resource intensive. If your system is close to the minimum system specifications, this can cause the connection to drop. Try disabling any other background programs including Steam, Skype, etc. to free up some more system resources!
Getting Us Your Log Files
If the above steps do not help, please try flushing your configuration files. Steps on how to do this can be found here.
If the issue persists after following the above steps and flushing your log files, we'll need you to send us your system information and logs using the directions here.