I follow all instructions on http://www.arduino.cc/en/Guide/Troubleshooting#upload
page. Can't imagine nothing more except buy another board. But exist so many people with this problem (just search google for the error message) that I am afraid. There must be SOMETHING that cause this (sadly, I lack the tecnical skills to discover it). Maybe a component malfunction. I just want to understand, so I can take more care. I didn't even connected nothing (except usb cable) on my board, and isn't working anymore. All I did was upload the ASCIITable example. After I disconnected the board from the USB, I tried it on a Vista machine, and after that, my problems begin.