Uno doesn't appear in Tools > Serial Port in Snow Leopard

Unpacked my new Uno today, and got it running for a while on my Mac, did the Blink program, etc. But now it looks like the USB connection has conked out. Under Tools > Serial Port, I only see /dev/[tty OR cu].Bluetooth-, where previously I had /dev/tty.usbmodem. I've tried different USB ports, rebooting, turning off Bluetooth, etc. to no avail.

The Uno still powers up and is running the Blink program that I had previously. Nothing Arduino-like (or usbmodem-like) appears in System Profiler > Hardware > USB. Based on some older forum posts I tried lsof | grep usbmodem, but it didn't find any results.

Is it possible that my Uno is fried so soon? Any other diagnostics I can try?

Try this:
Open up terminal (in applications/utilities)
type "ls /dev" without the quotes.
You should see a long list of things.
Now type "ls /dev/tty.*"
Post the results.

Weird. Maybe try a different USB cable? Or test with another computer?

baum:
Now type "ls /dev/tty.*"
Post the results.

/dev/tty.Bluetooth-Modem /dev/tty.Bluetooth-PDA-Sync

Which is consistent with what I see in Tools > Serial Port. Granted, in the Mac System Preferences > Bluetooth, I've turned Bluetooth off altogether, so I'm not sure why even these two appear. So is it possible that the PDA-Sync is interfering, and if so, how do I turn that process / connection off?

Thanks in advance!

mellis:
Weird. Maybe try a different USB cable? Or test with another computer?

Switched USB cables. No dice.

Then tried connecting to my wife's Windows machine (for which I have now installed Arduino software). When I got to Step 3 of the Getting Started w/ Arduino on Windows page (http://arduino.cc/en/Guide/Windows), plugging in the board causes the green power to light up (and the Blink program to start, just as it does when I plug into my Mac), but Windows doesn't begin its driver installation process as Step 4 suggests.

So this suggests to me that either the board or the AVR has a problem. Any suggestions? I do have an STK-500 at my disposal if someone can suggest steps to take on the ATmega328.

Which is consistent with what I see in Tools > Serial Port. Granted, in the Mac System Preferences > Bluetooth, I've turned Bluetooth off altogether, so I'm not sure why even these two appear. So is it possible that the PDA-Sync is interfering, and if so, how do I turn that process / connection off?

It is always on. IDK why.

And if you don't see anything on EITHER computer, it must be a problem with the atmega8u2 usb to serial converter.

bari_sax, check and reinstall the correct FTDI drivers and make sure they are unpacked not just downloaded, I have just run into that issue.

@baum: There definitely is some whitish-blue crustiness on one side of the ATmega8U2 (and a bit of white film elsewhere on the board). Not the black carbon of a burnout, but it looks a bit suspicious, so I cleaned the area with some alcohol and will let it dry overnight and see if maybe it was just a temporary short. Otherwise I guess it may be return time for this one.

@jrd210: I don't think reinstalling FTDI drivers is an option for the Uno, since it doesn't have an FTDI chip. I suppose it may be possible to update the ATmega8U2 firmware (http://arduino.cc/en/Hacking/DFUProgramming8U2) (assuming that would help), but I have a feeling that this is a bit of a Catch-22 if I can't communicate with the Uno over USB. Again, I could potentially hook up to it with my STK500, but I think at this point it may be less work to just replace the board unless someone has a better idea.

You could try following the DFU upgrade procedure. It's possible that there's a problem with the USB-serial (CDC) part of the 8U2 firmware (that's used to upload sketches) but that the DFU bootloader on the 8U2 is still okay. When you put the 8U2 in DFU mode, it's running other firmware and appearing to the computer as a different kind of device. Worth trying at least.