New screen, now cant make calls

[bug1]

Hi all;

I dropped my phone a while back, I got a replacement screen and installed it myself. First time on any phone...
I put it back together and the modem doesn't appear to be working, have reinstalled mobian, I have signal strength, but not registered on the network. Everything else seems to work WiFi is good.
Have tried different sim card, no change, sim works on other phone.
Is there anything I can do to narrow the fault down to software or hardware ?

I guess I must have stuffed the main board somehow when I pulled it apart, but it would be good if I could confirm it.

Thanks