The homelacie.com website locates an Ethernet Disk Mini: Home Edition or Internet Space drive by knowing its external IP address. As external IP addresses frequently change, the first thing to do when there are connectivity problems is to wait a couple hours.
If that doesn't solve the problem, try to locate the drive on the LAN if possible. To do this, the Ethernet Disk's internal IP address will be required. There are a few ways to locate an IP address, but the best way is to get the information from the router it is connecting to.
Most routers show a "client list" in their web administration screen. These show all drives on the network. Try connecting to the router through a web browser to se if this data is available. If the drive is listed, type its IP address in to a web browse (ex: 192.168.0.101)
If this fails as well, try some physical troubleshooting. After each test, try to connect again.