Are you sure that you haven't used up your membership allowances?
Can you receive calls/texts?
Can you use internet/data (not via wifi)?
Have you tried switching off, taking the sim out, gently cleaning it, reinserting it, switching on and trying to manually scan for networks and connecting to 48?
If necessary contact 48 support for more assistance:
http://help.48months.ie/requests/newHope this helps.