Hello everyone.
I have the same issues.
I have tried several 2560s (4), 3 Unos , several USB cables for both models.
The old 2560 and Uno were both working ok the last time I used them late last year.
I downloaded the new IDE software and that , I believe, is when my troubles started.
I am using an XP.
I hope the fix is not simply giving a replacement unit. As I have indicated earlier, I did that several times with the 2560s and Unos.
I will be watching this thread. I hope somebody will figure out what is going on.
T2p2