Accidently short the 5v and GND pin on my UNO.

I am just curious what was damaged. I accidently short the 5v and GND pin while I was connecting the USB cable to my pc. Thanks.

Then probably nothing and the PC just switched off the power to that USB port... If you connected it to a powered usb hub you might have blown the mosfet.

Thanks.

With USB power you are in luck. The Arduino has a self-resetting fuse that will prevent drawing more than 500 mA from the USB connector. It will reset if you unplug the USB for a few seconds.

That's true, the Uno has that as well :)