Now i can use the ralink wifi usb stick(i got help at http://ubuntuforums.org/showthread.php?t=2147236, thanks Chilly and Bucky Ball), but every time i start ubuntu, it can not identify the usb stick automatically. the "Enable wireless" option in the internet icon is shut down automatically. I have to plug the usb stick out and plug it in, then it will work. How can i solve it? Thanks.