SNR (>= 25)

Line attenuation ( 5 - 40 db)

Turn off power to your modem for 5 mins before reconnecting and see if your Signal to Noise Ratio (SNR) Margin for downstream becomes above 25 dB. If not, get your ISP tech to check out your phone lines and filters. A low SNR means noisy phone line that is disrupting internet signals.

Lay a new line

Problem may be in old phone lines or distance to the ISP's switch or both.