You probably need to modify your installation. Since SW2013, Visual Studio Tools for Applications support has not been included in the default installation options. This is because VSTA requires Microsoft.NET 3.5 which is not installed on Windows 8 by default and SOLIDWORKS is not permitted to install it as a pre-requisite.
Please visit https://msdn.microsoft.com/en-us/library/hh506443(v=vs.110).aspx to find instructions on how to install Microsoft.NET 3.5.
Once you've installed the framework, modify your SOLIDWORKS installation through Windows Control Panel and add the "Visual Studio Tools for Applications (VSTA)" option under SOLIDWORKS on the Product Selection page of the Installation Manager.
I hope this resolves your problem. Good luck.