I am using Arduino Uno R3 on windows 8. when i'm on sketch tools-> serial port->COM3.
only com3 i see. When I go to device manager on ports yellow exclamation point i see. Need help please.
What should I do? >:(
I think your problem is that the drivers aren't installed properly. You should be able to correct this by:
Going to the device manager and right clicking the device with the exclamation mark (presumably the Arduino) clicking properties and then navigating to the driver tab. Once there select update driver and then "browse my computer manually."
You will then need to select "let me pick the driver", click on "have disk" then browse and navigate to the Arduino.inf file under the Arduino install directory.
This should be in %systemdrive%/program files/arduino/drivers/arduino.inf or %systemdrive%/program files(x86)/arduino/drivers/arduino.ini . Depending on if your computer is 64bit or not.
Once you have selected the arduino.inf(arduino) file press ok, another ok and then chose your Arduino type and press next. It should install the driver without error.
If you have a 64bit computer you might also want to have a look at this article detailing the way to get your 64 bit pc to run unsigned drivers.