Hi,
This issue might occur due to the improper screen resolution settings or corrupted drivers.
Answer the below question to understand the issue better.
1. What is the make and model of your computer?
2. Did you make any recent changes before this issue occurred?
3. Do you face this issue with particular app or all the apps?
Try the steps in the following Microsoft Help article and check if it helps.
http://windows.microsoft.com/en-us/windows-8/what-troubleshoot-problems-app
Send us the screen shots of the issue to assist you better.
Reply with the status of the issue, I will be happy to help you.