Have you accidentally turned on "Sticky Keys"? If you have then follow the directions below:
"1. Navigate to Control Panel and click on Ease of Access center, and find the link for “Make the keyboard easier to use”.
2. Once you are there, you’ll want to make sure the boxes for “Turn on Sticky Keys” or “Turn on Filter Keys” are turned off—which simply means the feature isn’t active at the moment.
3. Further you’ll have to click on either “Set up Filter Keys” or “Set up Sticky Keys” (or both).
4. Disable Filter Keys Popup.
5. If you went to the Filter Keys setup screen, remove the checkbox from “Turn on Filter Keys when right SHIFT is pressed for 8 seconds”.
6. To disable Sticky Keys Popup, uncheck the box for “Turn on Sticky Keys when SHIFT is pressed five times”. "