If you are able to connect to it directly with a laptop over ethernet, you should be able run wireshark and see an ARP request when you plug the cable in. Reviewing the details of the ARP request will show you the IP address.
Here is a more detailed FAQ for background.
The 127.x.x.x is the default loopback address for TCP/IP so I doubt the PC will be able to talk to anything in that address range without some reconfiguring of the TCP/IP stack (assuming this is even possible).
In the EGX documentation there should be a section where it describes how to reset the gateway back to factory default communication settings using either a button somewhere the device or connecting to the serial port and then power cycling. If you can not find the documentation or it still does not work then a quick technical support call should resolve this.
Hi Ta Cong,
If you have access to the EGX100, the only way you may be able to master reset it is as outlined as follows:
This is located in the install guide. This will be the only way to do it without an RMA as far as I can see.
Read my mind - the answer I was going to provide. Some people also know how to use wire shark to spot the IP.