Working fine for me in Dublin 7. Try the usual switch off, take the SIM out, gently chav the contacts, reinsert it, switch on, manually search for networks and connect to 48. If that doesn't work then check that nothing changed on your phone - settings changes, software update etc. - that might have affected things. If all else fails then you'll have to contact 48 support for more information. See the link in my signature below.
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.