Why does my laptop keep connecting and disconnecting from the internet?

My laptop is connected to my cable, so it is not wireless. It is constantly connecting and disconnecting every minute or so and I lose whatever I am doing---including cutting me off from IMs and they think I am being rude by signing out while they are talking to me. Its a new laptop--although it is a cheaper one (acer). But I all ready exchanged the modem at the cable company--they thought it could be faulty---didn't help. Any help is appreciated.