I have a catalyst 3548xl with a 1000BASE-SX gbic module and I want to replace a failing dell Powerconnect. The problem is I am unable to connect the 3548 to the other dell with the fiber. The connection stays down and come up for a second when the dell is rebooted but then goes back down. If I place a second gbic module in the 3548 and connect it to the first one in that switch the both come up and connect yet I get nothing when connecting to either dell. Is there a change that needs to be made to one of the switches?