Different devices, such as UPS or print server have a web interface. Just a pity if you have purchased a used unit and the predecessor has adjusted the IP and thus it has no access..
Now there is a very simple way of finding out the IP yet. Using ARP Protocols and the tool Wireshark www.wireshark.org/
You connect the device with a crossover network cable to your network card from the computer directly. A standard network cable will work in most cases. You must complete each network program on your PC, Skype, …
Start Wireshark. Logging starts immediately. Then launch the device in question. You should be very soon a broadcast message from the ARP protocol of the device see in the info the IP address is displayed.
In this example it is the 172.20.103.171: