Is this windows 7 or 8?
If so, what setting is specified in the windows display control panel?
There's known issues with the display with FileMaker 13, windows that occurs when this setting is for any value but 100%.
And yes, this is a significant problem for some machines with HD displays.
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
It is Win 7 and yes it was set to 125%. I lowered it to 100% and all fine now. Thanks...