What phone do you have? You're not in airplane mode or anything like that? Set the network mode to the one with the most options, like say gsm/wcdma/lte or whatever. Go into network settings and selecting network go manual and wait for the list to populate after 1-2 minutes. Do you see a list of networks available to connect to? Try a few and see if you can connect. Aim for AT&T or T-Mobile.