I understand that even though the Slingbox shows solid lights (power on and network), you are not able to locate the Slingbox on your network.
The following link will provide you with all the information about the Slingbox lights.
The fact that the Slingbox shows solid lights means that the Slingbox is a healthy unit. In this case, the issue seems to be related to the security software running on your network. The following link will provide you with some steps to follow.