i have installed ubuntu 9.04 recently with dual boot. in windows the i can access the net but in ubuntu partition the ethernet card is not being detected

i have installed ubuntu 9.04 recently with dual boot. in the windows partition i can access the internet but in the ubuntu partition it cannot detect the ethernet card.i use broadband coonnection. my friends who have similarly installed ubuntu 9.04, could access the net with broadband connection but i cannot. first when i tried to connect it simply didnt. then i used the "sudo pppoeconf" command and then it said the following "sorry, i scanned 3 interfaces, but the access concentrator of your provider did not respond. please check your network and modem cables. another reason for your failure may also be running another pppoe process which controls the modem." so i cannot connect to the net.