There are a few reasons this happens, from the PC being overloaded to changing the display modes. There is a fix that may work , please fallow the steps bellow :
1. Go to your Control Panel.
2. Open Appearance and Personalization. (Or Appearence and Themes, depending on your Windows version.)
3. Click on Display, on the Settings tab click Advanced.
4. Next click on the Troubleshoot tab > Change settings , and move the Hardware acceleration slider control until you reach this message : "Disable all DirectDraw and Direct3D accelerations, as well as all cursor and advanced drawing accelerations. Use this setting to correct even severe problems with DirectX accelerated applications."