My Action Center tray icon is missing for a while and even after I right click and click properties on the tray, I can't turn it back on since it's grayed out. I tried methods of editing the registry, but no luck.
First, I would advise you not to tinker with registry unless you are absolutely certain what you are doing.
To your problem....
It may or may not help you, but give it a try.
In the system tray, do you see a triangle pointing upward ?
If yes, click it... click Customize... scroll down to find Action Center.... click the pointer at the far right, and select Show icon and notification... click OK when done.
Link to skydrive screenshot.......