Cash credit on your account has no bearing on internet working or not.
The only way internet works is with a valid membership and a non zero membership or data add-on allowance balance.
Double check the settings and other relevant details by following the instructions here:
http://community.48months.ie/t5/Need-Help/Internet/m-p/34493#M12560
If you still have problems please post back with more details - e.g. what your My 48 account page says about your membership status and expiry date, your data allowance balance, your internet/APN settings etc.
Hope this helps.
