Hello,
I have 2 Arduino Uno R3 boards. First works great and the problem is with the other board.
Problem is that i can't see the second board in Device Manager like the first board.
Another problem on that board is the "L" LED. When I connect board with PC, the "L" LED blinks constantly. So if somebody had the same problem, could you advice how to make this work?
Thanks
Warning, I am no computer tech extraordinaire. But I have had my share of issues with Arduino over the years.
Did you try plugging in the boards one at a time when trouble shooting?
Have you tried restarting your PC with the faulty Uno then updating its drivers?
Sounds like you may have a sketch running on the older Uno possibly from an earlier project and have since updated your Arduino software and the older board is not yet synced.
Something that worked for me is restarting the computer with only the UNO in question attached then re installing the software and erasing the older version. Then updating drivers on the board and restarting again.
I had issues with my PC's usb connection wiggling when I was adjusting hardware which kept disassociating the board with my PC so I had to restart often.
Let me know if this helps or falls on deaf ears.
Oh, Another thing.
Your other board may be showing up unknown under 'universal serial bus hub' as "unknown".
This would most likely be the device you want to update drivers on. It is also possible it is set to the wrong serial port if you wanted to fiddle with selecting a port your other board was working under to test.
To change the port select the "unknown" device under the tree "universal serial bus hub". Select properties, then port settings, then advanced and adjust the port to COM 3 or something similar that is not in use. Preferably use the port recognized by the other board.
Thanks for advice, i tried everything... Still at zero... 
I cannot upload my UNO board. I am using the Blink test1 sketch. I think I compiled and uploaded the first time because the same blinking rate is there. I tried one of my sketches and now I get the following:
avrdude: ser-open() can't open device "\.\com1: The system cannot find the file specified.
I had no problem with the software download. Everything seemed to be automatic. I uninstalled and downloaded again. I am using Windows 7 and the board is using com3. Everything looks good as far as the USB, "DEVICE WORKING", switching cables,and I even tried m Leonardo board. My Leonardo is using com5. I have switched USB jacks on my laptop. My board are happy blinking away, the green light is on but no upload.
Ask me some questions and I'll try anything
Rhodeman
Firstly MallHugo, where did you get your non working board from? Was it the same source as the working one? Does it have the Atmel chip for USB to serial as well as the Atmega328?
rhodeman, Same question. Where did you get your board from and what is the USB to serial converter?
I got both of them on faculty and everything works fine. Sorry i'm new with this.. You think on Atmel chip(a little left from RX/TX LEDS) or this (http://arduino.cc/en/Main/USBSerial)?
Could You see, I uploaded photo of my board in the first post.
Rhodeman,
Sounds like your port is pulling the wrong "Com". Unless i'm mistaken, you mentioned your Uno board states it is using "com3" under tools but your PC is stating "com1". Have you tried switching to "Com3" manually with your port ID as I described above?
Also, when you plug in your other board " leonardo", are you plugging the usb into the same port you plugged the Uno into?
If so, might I suggest plugging in the Uno into the same port, manually adjusting the "com" to 'com5' in the device manager and then updating the arduino port to 'com5'. You may need to restart your computer to have the arduino recognize the new port after manually adjusting the port and the verify in the device manager and the IDE software.
I've had a similar error when selecting the wrong port (com#) different from what the PC calls out for the actual usb port. But then again. I too have been having issues with uploading.
