Broadband internet problems

our computer network at home runs the internet through one main computer and the others connect to it…

however lately the internet keeps cutting out every 5 minutes or so and then takes 30 seconds to reload - as if it switches itself off and turns back on again… it’s really annoying trying to have convos on msn and just general usage…

i have no idea what’s causing it… can anyone help?

we normally leave the thing on 24/7 (unlimited downloads - why bother turning it off?)… but i turned it off one night recently and as soon as i turned it back on in the morning it did it again…

thanks very much in advance…

_dale