This is most likely a problem with your graphics card and/or driver. Check on the SolidWorks website to see what the approved driver is for your computer, card, and SW13. If your computer or card is old, there may not be an approved driver for SW13. Try the approved driver for the last version of SW tested. If that doesn't work, try other versions from the card maker's web site. If you are not running an approved card I would strongly suggest getting one.
This problem has been discussed in several threads, but I can't remember much about the discussion and can't think of the best words to search on.
That is typical on my systems when the Windows Aero theme becomes disabled. It happens occasionally for no obvious reason.
Re-enabling an Aero theme is the simple fix.
I have the same problem, mine even was in 2012 and 2013. Tried new graghics driver from SW and it didn't work. 2013 isn't as bad as 2012 was, except now I'll get a vertical cell also.
Are you using a Windows Aero desktop theme? What you see is an indication that you are not and need to.