Internet Keeps Disconnecting

Hello,

i don;t have a good knowledge on internet devices. last i connected internet that has a small device on the roof top to catch the signal and the wire that comes from the device goes to the spliiter like device, and through lan port new cable comes to my pc. on inside i connect the internet through dsl connection and it works fine and after some time the connection fails and i have to reconnect the dsl connection and sometimes it don;t work either. so can any one have solution for me?

i use ubuntu 9.04 and mozilla firefox 3.5. Thank You!