From here: https://support.microsoft.com/en-gb/help/2957623/cannot-access-shared-files-or-folders-on-a-drive-in-windows-server-201

Symptoms

To work around these issues, follow these steps:

1. Disable the leasing on the file server. To do this, run the following command:

   REG ADD HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanserver\parameters /v DisableLeasing /t REG_DWORD /d 1 /f 

   Note After you set this registry key, SMB2 leases are no longer granted, but oplocks are still available. This setting is primarily used for troubleshooting.
2. Restart the file server, or restart the server service. To restart the service, run the following commands:

   NET STOP SERVER
   NET START SERVER 

Some people recommend using ….control + alt + end on a RDP session to bring up that Windows Security screen, but it does NOT work on nested RDP sessions.

This procedure is the only one which worked for me on a Windows 2012 R2 RDP session:

1. Click Start
2. Type osk (to bring up the on screen keyboard)
3. Hit enter
4. Once the on screen keyboard is open, hold ctrl+Alt on your physical keyboard, then click on the del key in the on screen keyboard.
5. Minimize the on screen Keyboard
6. Click Change a password.

From here: http://devonenote.com/2013/09/how-to-find-startup-folder-in-windows-server-2012/

In Windows Server 2008 R2, to define an application to be startup automatically for current user, one common way is to create an application shortcut and add it to startup folder. In Windows Server 2012, you might find you can’t find this startup folder any more. 

Here is the steps to find startup folder in Windows Server 2012.

1. WinKey + C to open the charms bar
2. Click “Search”
3. Enter shell:startup and click on the first result returned.