Hello. I’ve never seen this on an iMac before. If the computer turns on but the screen stays black then you’ve probably got a broken LCD. If you don’t have a warranty then you could try replacing the LCD.
Hello. Yes I can confirm that the cellular and GPS screen work together. I did it myself and the both worked on each other. The cellular screen appears to have an extra antenna or something like that from what I can see.
Hello. Try restarting the update if you haven’t already (Hard reset the phone by holding home and power buttons together) Otherwise if you are able to force restart the phone it may cancel the update. Then you can backup all your photos and other data. After backing everything up connect the phone to iTunes and restore it. Then you will be able to restore the backed up files and have the phone updated too. Hopefully this works.
Hello. Sounds like you may have damaged some of the components on the motherboard. Check that all connectors are correctly connected and look for any possible damage to the motherboard. If it is damaged then your better off replacing it, but it could just be that the connectors are loose or not put on properly.