Are all cameras inside?
I found placement was key to getting a bright picture inside.
I don't think X10 cameras were designed for inside use as generally they don't perform well without lots of light, even the low light b&W models
You might want to try another piece of software for viewing your cameras on the PC, Vangard realy is low level.
The lines you are seeing is interference from another wireless device. The channels can be change on the cameras and receiver as well as phones and routers.
You could also mod your cameras to wired versions so you can truly run them direct I doubt that would help the dark issue though.