No Service after screen replacement

Hello,

Recently picked up an iPhone 6S plus with a cracked screen. Replaced the screen, put the phone back together, and powered it up. Everything is working, including WIFI antenna, but the phone shows "No Service". The SIM card has been placed into another phone and I was able to make and receive phone calls using the other phone. Even put another active SIM into the "problem" phone and still No Service. It is an unlocked Sprint phone. I've put the phone in "field test mode" and it seems the phone is not able to find a cell tower signal. I've checked the assembly and all plugs and connectors are good. The only issue is that I believe the battery cable was NOT disconnected during the initial disassembly. Thanks for the help!