Leftover screw

Fully disassemble the device and wipe the contacts on the ribbons and other connections with isopropyl alcohol. This type of lcd malfunction is usually caused by a short or an improperly seated/damaged ribbon, if it shorted then there's a good chance the lcd will need replacing, however I would clean it and re-seat everything first.

In this image: http://d3nevzfk7ii3be.cloudfront.net/igi... is the copper strip you severed in the bottom right immediately to the right of the circled screw holding the lcd in place? Because that's the volume/lock/power ribbon and ifixit has a guide for its replacement if that's what you're talking about. Edit: You're welcome.

It needs to be serviced, if it's not charging or turning on there's a hardware failure. A common issue is the charging port, after replacing, if it's damaged that is, then allows the phone to actually charge, but without more information it's hard to tell. Edit: I should add that you can't pull the data off until the phone is on, thus the hardware failure needs to be addressed.

Some solder has a higher melting point and can be quite difficult to remove in comparison to weaker solder that seemingly melts on touch. I personally pre-heat the area with a rework station then heat the solder and use a sucker and desoldering braid to clean up the board and remove leftover layers. I'd have to see a photo of the board to tell if it's toasted, maybe not. I accidentally overheated and warped/damaged a motherboard around the power jack and it still worked because the traces were ok, so there's a chance!

Time to re-open the device, make sure the lcd ribbon isn't pinched, all of it directly from the lcd must slide through the top of the frame. Also re-seat all ribbons after checking for debris. Could also be a bad or damaged replacement lcd.