The game itself has not changed in that time, so this must be some other factor.
Is this just in one particular saved game, or also in any new CK2 game you start?
HOI4 runs okay, you are sure?
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/EU4/settings.txt.
From your Documents/Paradox/EU4/logs/ folder, attach system.log .