Not 100% sure on this one but I can think of a couple of possibles to check. The actions menu normaly sits alongside,Layers,Channels ect & they show & hide together,but they can be seperated.Once you seperate them(Just click on the top name tag & drag away ) they act independantly of each other. On the off chance your action menu has been "ripped off",check the drop down windows menu for show/hide actions. If it still shows "hide actions" then check the bottom of your screen to see if you have accidently minimized it and its hiding in your status bar.