weak signal

:( i couldn't find any thread on this forum about 2100, but i think that 2100 belongs to this family of fones so im posting my question here. I went to a shop and ask them to unlock a 2100 which is my mother's fone. After unlocking, the signal seems to be weak. I mean, before the fone was unlock, the signal strength is good but now it seems that the indicator only reaches about 2 bars. Is there something wrong with the unlocking process??? the personnel on the shop doesn't know what went wrong or if there is really something wrong. the fone's never been dropped so im really wondering about this problem. thanks in advance for all your help mates!!! ;) ;)