title: Visual Studio 2017, Intellisense is not working
body: <p>I just upgraded from VS2015 to 2017, and intellisense highlighting of syntax errors has disappeared completely.
  I tried some suggestions found online, mainly <code>Edit-&gt;Intellisense-&gt;Refresh Local Cache</code>, but that option is not there anymore.</p>
  
  <p>Under Edit->Intellisense there is only <code>Quick info</code> which does nothing when I press it, and <code>toggle completion mode</code> which is greyed out</p>
  
  <p>I'm using Windows 10, C++ project. 
  Do I need to delete some old files from VS2015 in order for intellisense to work again? like the <code>VC.db</code> file?</p>
  
  <p>Thanks</p>