Has this always happened ever since you've had the game? Or only since what change or update?
Is this just in one particular campaign/save game? Or also in any new one you start?
After it happens can you start the game right up again okay? Or you need to wait a while, or reboot before it will run again?
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 attach your Documents/Paradox/CK2/settings.txt.
From your Documents/Paradox/CK2/logs/ folder, attach system.log .