Does this happen with every port? Have you tried a different cable?
thanks GreenBay42 for the reply, yes I've used other different cables. actually the other ports of the switch has a cable plugged in (server&other switches) and their working fine even if I transfer it to other ports. I'm just wondering why does the switch deny all connectionsw except for the original cables plugged into it. is there a setting for mac filtering or registration of something before I can connect?
Thank you. and I hope you understand my issue. many thanks again....