After reading hundreds of threads explaining how to solve this crappy problem, I've decided to kill myself...whoooooaaaaaa
no, i'm just gonna reinstall ubuntu...
I'm SOOOO disappointed!!! Ubuntu 9.04 never gave me any headache. On ubunut 11.04 though, after the first time i plugged the headphones the sound died forever.
I hate to upload upgrade ubuntu, i'm never going to do that again.