In this scenario, it can be many reasons to cause this problem, even the current user has enough authority to do anything on Report Manager. Please try to do trouble shooting as below:

  1. Run the browser as an Administrator.
  2. Add the Report Manager URL as Compatibility View settings.
  3. Use http://<servername>/reports instead of using Localhost.
  4. If the steps above still can't make you see the dropdown menu, it might caused by corrupt reportingservices.js file. Please try to restore this file on server.