That usually means that the game resolution isn’t jiving with fullscreen mode.
You can try:
- Navigate to the Starcraft II folder that is in your Documents folder.
- In the Starcraft II folder is a “Variables” or " Variables.txt" file.
- Open that and find “displaymode” and set ot equal to 1.
- Save and close the file. Relaunch SC2.
This will change the display mode from fullscreen to windowed-fullscreen which tends to be less picky about resolution.