Couple of things you can try. First, I'd do a System Restore and take your machine back to a point in time BEFORE the pink screens started.
One important warning about System Restore: it will uninstall programs and drivers that were installed after the date of the selected restore point. In other words, if you installed MPC on 12/24 (just as an example) but restore your machine to 12/23 or earlier, MPC will no longer be on the machine.
Second thing to try is another widely used free player called VLC. It plays just about anything without the need for extra codec packs. See if the pink screen problem is solved. If it is, then you might have a corrupt MPC or K-lite. You could always uninstall the current versions and reinstall fresh.
VideoLAN - VLC: Free streaming and multimedia solutions for all OS!