No network after installing Hoary

[Ingi Bjarni Skúlason]

Hi,
Yesterday i installed Ububtu Hoary and everything was ok. But when i 
tried to connect to the internet using Firefox or with an other internet 
program, it didn't work.  My network is configured via DHCP and it 
worked without problems in Ubuntu Warty.

I'm a newbie in Linux and i am not able to fix this, please help me.
My computer is useless without an internet connection.



Ingi Bjarni Skulason