My guess is that you are using Windows 7 or 8. If so:
Open the Windows Display control panel. Set the display to 100% and see if that clears up this issue.
For More Information see: FM13v02 - with fatal rendering issues!!!
This is one of many acknowledged bugs that can be found in the Known Bug List thread here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: https://www.dropbox.com/s/jt09b82i0xijbu3/FMP%20Bugs.zip
I have the same problem. Clicking the zoom button temporarily solves the problem. but when I go back to 100% zoom, I continue to have the problem. I called tech support and they recommended uninstall/ reinstall FM but that did not solve the problem.