Maybe there is a ISP device converting from fiber to ehernet, as ethernet cable is mentioned.
If this is the case, the procedure is the same, only instead of sfp you make sure that ether1 is out of the bridge, categorized as WAN and has a DHCP client running.
Anyway it would be much better/easier if you could post more details on your layout and your current configuration, following these instructions:
http://forum.mikrotik.com/t/forum-rules/173010/1