Did a little looking around and it would appear that many people have the same issue but for different reasons.
The simplest is to reduce your HW acceleration to see if it's a video driver issue.
Right click Desktop. Select Properties>Settings Tab>Advanced Button>Troubleshoot Tab. Slide it all the way to the left. Check to make sure you're not using a high contrast color scheme as well.
If you have Norton installed, you may want to try disabling the Office plug-in to see if it fixes it.
The "How To" is here.
Some people have had to just plain uninstall it though.