Ok. This makes no sense to me. Recently the cable modem would not sync. The only time now that the modem will sync is if the main cable line from the street is plugged into it. Its been working fine up until now with the splitter. I have now tried 2 different splitters and 3 different cables and the cable light will only flash, not sync. As soon as I plug the main line in directly it syncs almost immediately and we have a fast connection.