internet problem

hey everyone ive got a problem maybe one of you can help me out. im having problem with my internet connection some times it just suddenly cuts off and stop working.i try to turn off my adsl modem and my router it still doesnt work so i have to restart my domain server all the time i get this problem, then only after that will it work again. any idea whats causing this problem.when it cuts off i call my lan provider to check if the prob is on there side they say there system is working fine.i get this problem almost 3 times every day.
tanx