You'll need to post a bit more info. What exactly happens? Any error message (s)? Can you do a manual search for networks and, if so, what ones do you see? If you see 48 can you connect? Have you tried taking the SIM out and gently cleaning the contacts before trying again?
Hope this helps.
I am not a 48 employee so if you need to contact 48 support then use option 3 or the chat facility here.