I can't see Object Explorer in SSMS 2012

Question

I'm writing an Addin for SSMS 2012 to create a custom Object Explorer tree context menu , unfortunately after I execute the code, the object explorer disappears and I can't show it even if i press on F8.

the code:

public void OnConnection(object application, ext_ConnectMode connectMode, 
  object  addInInst, ref Array custom)
{
    string toolsMenuName = "Tools";
    addInInstance = (AddIn)addInInst;
    applicationObject = (DTE2)addInInstance.DTE;

    objExplorerService = (ObjectExplorerService)ServiceCache.ServiceProvider
      .GetService(typeof(Microsoft.SqlServer.Management.UI.VSIntegration
      .ObjectExplorer.IObjectExplorerService)); 
}

thanks!!