Attached is a screenshot to provide some perspective. I have UNO ( R3,dowloaded the latest software (1.04) and installed the driver(arduino.inf).
i have win & 64-bit and had to install legacy hardware to show ports on device manager. Still the comp recognizes UNO as an unknown device and trying to update that particular driver fails to read arduino.inf. also tried to screw around with the FTDI drivers no use.
Please help !!!
Did you install the 'Arduino UNO REV3.inf' driver from arduino-1.0.4\drivers?
-Luke
there is no REV R3.inf in drivers folder, however there is one in Old_arduino_Drivers.zip. I've tried that but no use it still recognizes it as an Unknown device...
Maybe you still didn't tried everything 
http://arduino.cc/forum/index.php/topic,118440.0.html
If it does not work, then maybe it is something wrong with the ftdi
eried:
If it does not work, then maybe it is something wrong with the ftdi
Except that a "Uno" doesn't have an FTDI.
plug in Uno, wait for Windows to fail
Start menu
Control Panel
Sys/Security
Dev Manager
Ports
open port = Arduino Uno (COM #)
right click
update driver software
browse my computer
navigate to and select ArduinoUNO.inf located in drivers folder
.
tried the link.. no use
also uno is being recognized as "unknown device" under usb.
it refuses to update driver to arduino.inf and gives error as file is not supported by win 64 bit
i don't have any option of ports and com and can ONLY add them by adding LEGACY HARDWARE !
HELP !!!
What is the Hardware ID for the unknown device?
Go to Device Manager
Right Click unknown device
Select Properties
Select Details tab
Change Property to Hardware Ids
What is displayed under Value?
Adding it through Legacy hardware is not going to work. We need the hardware ID to be sure.
Do you know this is an official Uno R3 and not a clone? If it is, it may be using different guts. An Uno should have 2 Atmel chips, the big one in the center and a really small one near the USB port which controls the USB connection and provides the USB serial port.
You're going to have to delete that com port because when you get the driver installed correctly the unknown device will move up there as a com port.
Hello there,Even i'm facing the same problem with my new Arduino UNO. Steps i did after buying UNO as follows,
1)Refered arduino blinking led program and dumped code successfully to UNO and led blinks from port 13.I selected UNO board type,baudrate of 9600,serial port COM7.
2)Next day,when i connect it to pc,its detected as COM7 at ports in device manager.Then i tried simple ''hello world'' program from this website.But when i upload code to UNO i got error message as ''avrdude: stk500_getsync(): not in sync: resp=0x00 error''.
3)Now my pc is not detecting the UNO and it shows ''unknown device'' in device manager.
4)if i uninstall the driver and try to reinstall the driver,pc shows ''device driver is already installed''.
If its a problem of hardware,how can we check it?? How to check ATMEGA328P-PU ic on UNO board works fine or not?
Guys i don't know how to proceed now.Can anybody help us ??
Thanks in advance 