Why Windows Server remotely shutdown/reboot failed?

This is attempt to reboot a MS Windows Server 2008 R2. I tried to use "Shutdown.exe' and also "PSShutdown.exe", but both methods failed.
This is how I tried:

       a. I logged as member of domain admin on my laptop (Windows 7)
       b. open command prompt, type "psexec \\w2k8r2Server cmd"; connection successfully      *w2k8r2server is the target server
       c. in c:\windows\system32, type "shutdown -r -f"
   
          A system shutdown is in progress. (1115)

      However, system is not rebooting. Later I tried the PSShutdown, same result.

According to some forums, I even "pskill winlogon" and then "pskill trustedinstaller". still same result.

Besides Remote registry service, any services, such as, remote administration and firewall ports need to open?

Please help.