Help plz - my unlocked phone no longer picking up network!!

[nastyrose]

hi guys - new to here and iphone actually. really hoping someone can help me. i just bought an iphone, got it unlocked by a third party and it was working good. i have no idea what he used to unlock it or version firmware etc. i just know it's the 8gb (sorr)
so i was using it - downloaded songs via itunes 7.4.2, and then last night was putting some vids from youtube onto it - everything played well. then went to sleep and - BOOM! - this morning no signal for the network - name of network not registering and the date and time is still from last night (!) wtf? i tried reinserting the sim - it picked up the network for a coupla minutes then the signal and network disappeared again...
what's going on plz - what did i do wrong and how to undo??
thnx so much for any help
p.s - i'm in barbados, using a network called 'digicel'. i haven't fiddled around with anything else on the phone really, just the music, photos and videos..