Go to Edit > Preferences > Performance (Lightroom > Preferences > Performance on a Mac), and uncheck Use graphics processor.
Thank you for the reply. I have no drop down boxes of any kind to choose from. The only edit option I have is when I click on the photo and there is a small box that says edit and it opens a page of strange graphics. What am I doing wrong?
If you can't see the menu bar, press Shift+F once or twice.