Has this game ever run on this machine? Or never yet?
DXDIAG is a program you run from a command prompt or the Windows start menu 'run' dialog box (or 'search programs' in Windows 7 or later). After running it will open a window and start collecting info with a progress bar in the lower-left corner. When it completes click the 'save all information' button and save it to a file then attach that file here.
Please send in the game log C:\Users\<UserName>\AppData\Local\Introversion\Prison Architect\debug.txt
To see the AppData folder you'll need to enable View Hidden Items in File Explorer.