Loud noise from valve cover. Engine lost power, eventually would not turn-over.

Ok. Define 'not turn over'. To me that means either you're hearing a click from the starter and/or solenoid, or not. Have you checked the battery? Do the lights work?

If the noise came from under the valve cover, you're going to have to pull the valve (camshaft) cover and see what it was. It could be a valve or a valve spring. Or something worse.