If any of the system icons are out, you can re-enable them as follows:
Right click on the taskbar and select properties. This will bring up the "Taskbar and start menu properties" tab. This is where you mentioned it was greyed out. That's fine...From here you can click on customize button in the icons section. Locate the icon that you are missing and check status. The status type should read "Hideicon and notifications", change this to "Show icon and notifications".
If this doesn't fix the issue you most likely have an issue with a group policy on your machine. This can be fixed by following the instructions on the following link: