Loop Back Success / Upload Failure

Using Arduino IDE 1.x
1

Hi,
I tried the loop back test with my Arduino Uno and it works. But, when I try it with my Arduino Mega 2560 it the test fails.

When I try to upload anything to the this board, it doesn't respond and status keeps saying "uploading..." forever.

The board's driver is installed, the correct port can be seen in the Tools tab. I am not sure what is wrong.

I have been using the same board previously and it was working fine. Somewhere, I messed something up and here I am now.

Please help.

2

If the loopback test fails on the 'different computer' for one Mega, there is something wrong in the path from the PC through the 16U2 micro (the 'usb' micro) back to the PC.

I think it's safe to exclude the cable; so that leaves bad contacts (including bad soldering) on the board or a 16U2 that has lost its code.

You might want to provide some details for those in the know (I'm not one of them).

OS and IDE version on both PCs?
Are the Megas genuine or clones?