I have the same problem... Can no longer upload ANY sketches to Arduino Mega 2560 - timeout at upload - IDE 1.x - Arduino Forum
board passes the loopback test. reset button doesn't cause orange L to flash. worked perfectly for weeks, sudden problem, not sure what changed. burn bootloader fails, same error: usbdev_open(): did not find ant USB device.
other arduino works fine in same environment.
broken arduino produces same error on other machines