I am not sure what picture I needed. Several time ago I have same experience, but this problem fix by itself when I restart my PC. May be you need reinstall your MT5.
But before that you can try to force stop metatester to give some space of memory. To do that, press Ctrl+Alt+Del, and then select metatester that running.
My tentative conclusion is not enough memory.
May be another member can help your problem.