If you had something replaced a week ago, and that’s when the change in behaviour started, I would enquire with whoever carried out the work and ask them to fix it. If it came to me like that, one week after a battery replacement, I would replace the battery regardless of what any app told me and work my way through the list of possible faults from there. This is the best thing for you to do , i think.
The screws near the battery connector pass through the board to mounts on the housing of the phone so I don’t think you have damaged the board there as another post mentions. If you haven’t yet, try booting the phone without the battery and without the front camera assembly. A damaged front camera can throw up some weird errors if it was damaged during the repair. It’s a long shot but a heck of a lot better than the next fault i’m about to mention. . . If you got the screws mixed up when putting the shield over the screen connections, you may have long screw damaged the board there. With the screen removed and the charge port facing your body, check the bottom right screw hole for the screen connection shield. If a long screw has been screwed into that hole you may have destroyed a connection path in one of the boards layers. Not an easy repair, but a reputable shop should be able to help in this case. How to resolve bootloop problem (long screw damage) iPhone 5s
Before replacing the display (especially if it doesn’t have any physical damage), try a button combination to reset the phone. S6 is notorious for becoming unresponsive for no reason (in my experience anyway)... Power + home + volume down will take you to download mode with an option to reboot the phone. Hope this helps.
Don’t fret. Power down the device, double check all of your connections and try again. If you still get no display, troubleshoot with a known working screen. You can try the old one if it still has display or order a new screen to test again. Try not to damage the screen you are using because you may be entitled to a warranty return. It’s usually just a faulty part which can happen sometimes.
This is a shot in the dark but the home button, if you can’t see any physical damage, might be the screen causing the issue since it is routed through the screen to the motherboard. The volume flex cable runs along the interior of the phone behind the battery and may have come partially unplugged (since other functions on the cable are still working) or the flex itself is damaged (sliced, stabbed, etc.). Unlikely but it can happen. I don’t have any ideas on the front camera assembly issues but I would try a new screen with your old front cam to be sure the errors aren’t being caused by a sub par screen. Even just test with the old screen if it still has touch/display. I’ve lost count of the weird errors an inferior screen can throw up. Sorry I can’t really help more than just throwing some troubleshooting ideas your way .. Hope you get a definitive answer soon.
Screen is repairable but usually more expensive than previous models. I recommend Apple due to the fact that you can retain your warranty and the phone is still quite new. Iphones with broken screens usually go into disabled mode when the touch function is triggering itself due to the damage and it inputs the passcode wrong too many times. You can recover through itunes but you may have lost your data if it isn’t backed up.
The g935 is a curved screen; No, it will not fit a g930 phone... That's like pushing a square peg through a circular hole .. Like why won't a bike tire fit my car? They are both tires, right? ... Just expect every model of phone to have it's own screen and none of them are compatible with each other. There are exceptions to the rule, of course, but you will save yourself some grief if you accept the fact. Are you looking for parts or a repair? Are you only looking in the one place if it's for parts? If you check with a number of different suppliers, the prices will vary. In my experience the g930 is the less expensive of the two models to repair so the prices you have been given are strange to me.
Long screw damage is not something your regular home repairer should attempt to fix. It sounds like you definitely have board damage. If you post your general location, I'm sure there are micro-solderers near you that can do the repair or at least point you in the right direction to find someone who can.