My first guess that if you are on dial up it is some thing your ISP is doing. The way that dial up ISPs and broadband ISPs handle incoming traffic is very different, and broadband ISPs are usually designed to handle more traffic than dial up ISPs, so a dial up ISP may be more protective about it's lines than broadband ISPs.
First contact your provider and see if it their policy that is kicking you off. If not it could be a phone line problem.