BC548C wrote: What worked? The uploading of programs or the program you have in it?
At the time you had it working, how did you have it powered, USB or power supply?
If you only powered via USB, try a separate power supply to know if you damaged the USB fuse.
Does your UNO have any LED's that come on when powered?
Have you tried a diffeent USB cable?
Does the program you have in the Arduino give any indication, say via LED's or serial as part of the program?
If the problem is that you are not able to upload to it anymore, and you have tried other computers, and all the things above, then I can only suggest either you try to see if you can re-program it via an ISP programmer or replace it.
I ran some programs on the uno, and actually now when I make the same setup it's still working.
I powered via USB & power supply and both working.
The green Led is working and in the beginning the L-LED is blinking for 1 sec and than stays on.
And yes, tried with different USB-cables...
The program that is running now is with servos and still is working.
I can't upload anything because the uno is invisible for each mac/pc I think.
Do you got some more information about the ISP programmer?
A friend came by with his arduino Uno and got visible immediately and is working on my mac/ his mac.