Motorola surf-board sb6121 receiving connection, but not sending. I have comcast, just internet. While setting it up, I found The previous tenants were using a entry series evo1-5-u/u amp, but it doesn't have a power box now, so I took the main line form the input and plugged it into the modem. This caused the modem to show a green light for receiving data, but the one beneath it, for sending, blinks blue. What could it be?