If you're not sure what IP addresses are in use on your network, try one of the following software tools:
SoftPerfect Network Scanner
You can download SoftPerfect Network Scanner here. Simple extract the zip file and run the appropriate 32-bit or 64-bit version.
Set the IP range to suit your network. For most people, it should default to the same subnet as your PC uses. If not, set the range using the from and to edit boxes. If your LAN's subnet is 192.168.0.x , then set the from as 192.168.0.1 and the to as 192.168.0.255 and press the green arrow.
You can download Fing for Android devices (smart phones, etc) here.
There is also an Apple (iPhone, iPad, etc) version here.