Arduino UNO r3 usb device not found

I have problem when i connect my Arduino UNO r3 I got the message"usb device not recornized". I tried [u]1.change usb cable[/u] [u]2.install driver in folder drivers(not work)[/u] [u]3. Press reset button[/u] [u]4. Change Pc[/u] [u]5.Change OS-use ubuntu(have same problem)[/u] [u]6.Change IDE[/u] Before problem my arduino dropped from a height of 20 sm.Led power work. Сan be the cause of the crystal oscillator? :confused: