Two quick ones... (do a search)
"repair" (Windows programs/features - change)
"resetting" (Windows registry, open regedit rename solidworks key -old)
we had the same problem on some clients with SolidWorks 2014 SP5. Please see the following article at Microsoft:
Try to edit the registry as shown (for the time your installation is running) and after that try to repair your installation from the application wizard. This method also works if you have problems installing Draftsight 2015.
Hopefully this will help you...