Windows Experience Index - blank?

Took me a while to find this. If you're unable to update your Windows Experience Index score because the "Performance Information and Tools" window is just blank, etc., here's what worked for me:

• Click Start, type regedit.exe and press ENTER
• Navigate to the following location:
  HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Control Panel\Performance Control Panel
• In the right-pane, look for the value named "PerfcplEnabled" and delete it, if found.
• Also, delete the "PerfcplEnabled" value from the following key:
  HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\Windows\Control Panel\Performance Control Panel

Note - didn't find the value under HKCU but didn't matter; after deleting it from HKLM everything came back and started working again.