Cable internet although pretty simple there is a little thing that us cable technicians fight and that is ingress. This can be caused by older televisions, old copper braided cable wiring (radio shack), or loose fittings. This will screw up internet connection within the cable modem and causing the modem to drop off call your local cable provider and tell them you have intermitten connectivity and they have the proper tools to find where the ingress is coming from.