I've been using an UNO with a DIP processor for a few weeks - going very well. Acquired a new UNO, SMP edition, that blinks the "L" LED but will not talk with through COM 3 that works well with the other. When first plugged in, Win-XP recognized the new peripheral and I clicked on "install drivers" and Win-XP now doesn't flag when the SMP UNO gets plugged in.
I tried all the COM baud rates and have tried the procedures that work with the other UNO: IDE simply can't find COM3 when the SMP UNO is plugged into it, with its "L" LED blinking. Restarting the IDE & SMP UNO over and over that works with the other UNO hasn't worked for this one. Under the IDE Tools: Board there is only one Arduino UNO. Am I missing something?