I get the following error when i try to upload any code to my arduino.
Previously i tried to upgrade my firmware but since this problem occurred, now i uploaded my original firmware .
Still cant upload any codes.
Arduino: 1.6.4 (Windows 7), Board: "Arduino Uno"
Sketch uses 1,030 bytes (3%) of program storage space. Maximum is 32,256 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2,039 bytes for local variables. Maximum is 2,048 bytes.
avrdude: ser_open(): can't open device "\.\COM3": The system cannot find the file specified.
Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
Error opening serial port 'COM3'. (Port not found)
This report would have more information with
"Show verbose output during compilation"
enabled in File > Preferences.
What port did you select from Tools->Port? How did you determine that was the port for the Arduino?
johnwasser:
What port did you select from Tools->Port? How did you determine that was the port for the Arduino?
when i connect arduino to my pc , its under tools>serial port>com3
Isaac96:
A few things to check:
- Is the Arduino powered up?
- Does it show up in Device Manager under Ports(COM and LPT) ?
Arduino is powered up 
it does not show up in device manager
Actually i uninstalled the 1.6.4 version and installed 1.0.5 and it worked...!!! everything is uploading.
and idk what happened but the comport 3 changed to comport 4.
i mean previously it used to show (on lower right side of the IDE) Arduino uno on COM3 and now it shows Arduino uno on COM4.
Actually, I have a port "COM3" that always shows up on my PC even with nothing plugged in. It may be the 1394 port. But it shows up in the Arduino software but not in Device Manager.