You do NOT need a hub or switch to connect a network device to your PC. Just plug it directly into the CAT5 port (assuming your PC has one).
Assuming the device uses DHCP to be assigned an IP address from your router, log into your router and look at the connections list. This is never in the same place and you will have to hunt for it in the router docs. Failing that,
Some devices default to an IP address on the wrong network. E.g. if you are on 192.168.0.x and the device starts at 192.168.1.2 then you can't reach it and none of the above will find it. Or perhaps you just don't know what the IP address is but you DO know the mac address. The MAC address is often used as a serial number. If you see a set of 6, two digit, hexadecimal numbers on the case, that's probably the MAC address.
Also, MAC addresses start with codes specific to the MFGR. So if you know who made it, you can probably find at least the first 3 numbers of the MAC. See:
Since Ethernet actually works on MAC address and not IP, if the device is on the same physical connection as your computer (e.g. plugged straight in or on the same switch or hub) then you can just add an arp entry manually to assign an IP to the MAC, and then you can access the device via IP.
arp -s Inetaddr Etheraddr [ifaceaddr] Adds a static entry to the arp cache that resolves the IP address Inetaddr to the physical address Etheraddr. To add a static arp cache entry to the table for a specific interface, use the ifaceaddr parameter where ifaceaddr is an IP address assigned to the interface.
Note that you have to get it on the right interface adapter. use ipconfig or ifconfig to find the ip address of the adapter where the device is connected and then specify that as the ifaceaddr
This is a temporary fix, which will only last as long as the arp cache. e.g. when you restart, or change your adapter, it's gone. Just use it to get into the device and switch to DHCP or assign a different IP address.
Instead of the standard ping ip_address use ping -l 200 ip on Windows and ping -s 200 ip on Linux / Mac.