I assume your referring to a set of sling links.
Make sure you have them both plugged directly into power outlets and are NOT using any type of surge/spike or filtered power strips.
As stated in the manual:
IMPORTANT: Because the Bridge sends data over the power lines of your
house, plug the Bridge directly into an electrical outlet. Do not plug the device
into a UPS or power strip with surge protection. The Bridge has its own power
filter for protection against surges.
Are you using the configuration/network utility that shoipped with the sling links? (It's not really necessary; however if being used the mac addresses of both sling components must be set in the utility. If not, the won't communicate.