Perhaps you could tell us what kind of usb devices and more about the
circumstances. Do they never work? Sometimes work? Is it limited to some
usb devices or all? Usually usb devices in Linux are mounted or
made available as needed. My scanner does not show until such time as I try
to use it. If I plug in a usb drive or one with a memory card such as my
e-reader then it will momentarily show in the notification area, but then
it tends to sit there until it is needed. Usb devices behave differently
depending on the device and the situation.