I cannot play the Civilization V demo on my PC (Windows 7, with DirectX 11); when launching, the game window is displayed briefly and then it dissapears. How can I troubleshoot? Is there a game log file?
You can start by checking the Event Log Viewer. To open it, click the Windows "Start" button or press the Windows key on your keyboard to open the start menu. On the right hand side, about halfway down, you should see "Computer". Right click it and choose "Manage" (you have to be an administrator to open this panel). In the "Computer Management" window that opens, there's an "Event Viewer" entry under "System Tools". Expand that, then expand "Windows Logs". Now click on "Application" (see below for screenshot). Look here for anything related to Civilization 5, or maybe DirectX. Especially look for errors (the red exclamation point) as the Information entries probably won't be all that useful. If you do find a related log entry, then check the error message and error code, then google those to find out what's happening and how to fix it.