I just replaced the home button on my iPhone 4. When I put it back together and powered it up, the screen lit up with a...

Yes, it is a common mistake to pry the silver bezel from the back. You must be sure to pry the glass from the bezel. If you look carefully, you will see there is a thin rubber gasket between the glass and the bezel. The knife idea will work. The rubber gasket will get damaged, but since you are replacing the screen and a new screen comes with a gasket, that should be fine. Try not to scratch the silver bezel, though.

Have you checked the breaker? I assume you found the breaker and turned it off when you changed the outlet, but you didn't mention it. If no breakers are popped, you may want to check to see if this outlet is tied to a gfci outlet. It could be that the gfci needs to be reset.