A blank rectangle

Why am I getting a blank rectangle blotting out most of my screen with no way of getting rid of it unless I shut down, I use windows 7. HELP

Hello Janina,

We're happy to help.
Do you think AVG caused the issue? If yes, please tell us what makes you suspect AVG.
Could you please share the screenshot of it to investigate further? 
Refer to this article for the steps to capture the screenshot.
You can post the screenshot here on your topic. Click on 'Answer' & then click on the 'Image' [mountain symbol] & follow the instructions.
Thank you.