I'm trying to configure a fiber trunk between a Catalyst 3560 switch (Gi0/1) and Catalyst 3750 switch (Gi2/0/50). The SFP modules (GLC-SX-MM) are seated and the cables appear connected fine, but I get no green LED lights on either switch. Port settings for both are: status enabled, duplex: auto, speed: auto, portfast: disabled, flow ctrl (receive): off. I do have fiber trunks on other SFPs working fine. What troubleshooting steps should I take to bring the fiber trunk up to "Duplex Full, speed: 1000 ?