Re: Powerconnect 2748 - Unable to connect to Management Site.
The button toggles between managed and unmanaged mode. When the LED is lit it is in managed mode. When you toggle it from managed, to unmanaged, to managed, the IP address is reset back to 192.168.2.1. The switch reboot to change modes, so it may take a minute or so before it is pingable.
Is your PC on the 192.168.2.x subnet when you try to ping the switch?