Uno not recognized by windows

Development Tools IDE 1.x
1

I've got two Unos (R3) that I'm having problems with

  1. When you plug in the USB cable, the green power light comes on, the pin 13 LED flashed a couple times and then turns on steady, but it's not recognized by the Arduino IDE. It was working at one point, I don't see any physical signs of damage (e.g. burnt chip) and the project it was being used for shouldn't have pulled too much current, but it's been tried on 3 different computers all of which successfully connect to other Arduino Unos. I read through the troubleshooting FAQ and nothing seemed applicable there. Just wondering if there are additional ideas out there

  2. Different Arduino Uno - for a project I built a balancing robot. The motors are powered by the adafruit motorshield which has its own power source. Generally downloading new code and using the serial monitor is not an issue, but over the last couple of days the robot will be running (I'll have the serial monitor open) and the serial output freezes and then if I try to download new code or close and re-open the serial monitor, I get an error message that Serial port 'COM3' not found. In order to get it to re-connect, I have to unplug the USB cable from the Arduino AND close the IDE and then re-open and re-connect (just closing and re-opening or disconnecting/reconnecting doesn't fix it--both have to be done). When I re-open it it works for a while (seemly random how long it works for) and then it happens again. I tried it on a different computer (a Macbook) and the issue seemed to go away. I thought it might be power issues, but like I say, the motors themselves are powered separately from the Arduino. Any ideas?

In both cases, Arduino IDE 1.0.1 on Windows 7
Thanks

2

Is it possible to order replacement some of the custom components for the arduino? For the first problem mentioned above, I'd like to replace the ATMega 16U2 but I assume it's custom programmed and can't just be ordered from Digikey or Mouser, etc.

I've also got a different Arduino Uno (I've got 10 kits for digital controls class I TA'd) that a couple pins appear to be burned out and I think if I could get a replacement ATMega328 with the bootloader already burned to it that would be awesome (I don't have any equipment to do that and as much as I would like to get it and learn how to do that, now in not the time)...I know it's probably just as easy to order a couple new boards, but there is a strange satisfaction in repairing the boards...