Touchscreen, power button, volume button, and mute button not working.

You do not need to go to apple for this problem. It is not a security problem. None of these parts need reprogramming.

@imicrosoldering Thanks! I agree with you.

I do know that apple phones from the last 5 years at lease have this issue with replacement parts. yours may not and I hope it doesn't.

Those flex cables are a pain. when you insert them in having a small piece of non-conductive tape on it can help you hold it in place while you lock it down. insert at no more than about 30° or it may catch on the feeler pins and not go in all the way. I put the tape between ¼-½" (6mm-13mm) from the end so that when seated a quick lay down and press temporarily holds it.

be sure the ribbon is parallel looking to the lock and doesn't wonder up or down even a little. those feelers are very tiny.

Also before you try it again check the lock for debris! even a tiny lint piece will give you loads of issues. Also check the solder joints with a magnifying something like a different HD camera phone or magnifying glass. Your looking for almost imperceptible hair line cracks. If you see one use a soldering pen and briefly re-melt just that one spot. Use a really fine tip and don't touch the plastic lock body at all.

The screen issue is probably the ribbon almost seated but only on the edge of one side. unlock it and push until parallel and tape. look at it and if it looks well seated lock it. test the screen before you reassemble it again. also jiggle screen and test but don't tug on the ribbon. I have seen ribbons have a wire pulled under the insulation before and this acts just like this.

EDIT: oh and check the ribbon for damage on the buttons and also were it attaches to the daughter board holding the buttons. also check the solder for cracks or weird bending on the daughter board and the solder itself as sometimes it connects across 2 pads and this will prevent operation and could damage it depending on how much power it has.

also when you take it apart next take some pictures so I can see the connections and the daughter board from different angles.

This is just a maybe but if you have a OHM meter you should be able to test the buttons. tape a couple of dulled needles to the probes and test each combination. it should not have anything unless they designed it weird. than using something like paper on the button tape it down firmly and retest. you should be able to find each button on the ribbon end and if you do than the buttons are fine. inspect lock and clean. some non-conductive fast dry electronics cleaner can help knock out anything and even can knock off corrosion.

Chris Stables BTW screens will do this if they aren't registered in the firmware on some models. I didn't see that it worked find before so yes he will not need to reprogram it.