Ubuntu sometimes stops responding

[Diogo Branco]

Hi all, i have Ubuntu version 9.04 64 bits, sometimes when i am
browsing the web with firefox 3.0 or shiretoko 3.5, the ubuntu machine
stops responding i have to press reset button of the computer to
restart the machine, i cannot find anything in the logs, my board is
an asus p5b-e i dont know if is there any issues with this board and
ubuntu i hoppe not.

Regards, Diogo.