focusrite scarlett 2i2 - no output

how do you repair usb drivers or down load new ones for mac book pro 10.8.4

Any updated drivers would have been included in, downloaded and installed with the 10.8.4 update.
There is nothing further for you to do.
You do not need to go looking for updated drivers for OS X.

What is it you want to do or issue you are having?

usb

use a midi device and the sound does not come out but the input goes in

Would suggest you make a request for advice on the specific device you are attempting to use and I can rename this thread and move it to the appropriate forum.

midi

the device is focusrite scarlett 2i2

Do not use any midi devices myself, so only question I have is did you open up Sound Preferences and select it as the input device?

(new title and moved - you can see the new location in red at the top of the thread)

What software are you using? This isn't my area of specialty either, but when I want to use my USB-based Snoball rather than the built-in Mic, I have to go into Audio/MIDI setup in Garageband (or Amadeus Pro or whatever) and change the input. Are you doing that?