Check the Arduino Troubleshooting page to see if there is a solution to your problem. Also, consult the idea below
Problem: Can't upload. Solution 1: Assign the correct serial port. In the Arduino Environment program, Tools > Serial Port, and select the correct serial port.
To see what serial port the board is using, connect the board to your computer with the USB cable. From the Windows desktop, right-click on My Computer. Then Properties > Hardware, Device Manager > Ports (COM & LPT). There will be an entry like "USB Serial Port (COM4)". This means serial comm port 4 is the one in use.
Problem: On upload, get error msgs like, avrdude: stk500_getsync(): not in sync: resp=0x30. Solution 1: Go into Tools > Serial Port and select the proper serial port. Solution 2: It is possible that the FTDI drivers were not installed correctly. Install again, carefully looking at the proper dialog box entries in the instructions. Solution 3: Iterate the Com port to some higher value in the Windows Device Manager, by selecting Properties -> Port Settings -> Advanced -> COM Port Number. Click OK, select the new com port value in Arduino.exe and see if the upload works. Solution 4: Consult the Arduino upload trouble shooting page.
Problem: On upload, get error msgs like, Serial port 'COM4' already in use. Try quitting any programs that may be using it. Soultion 1: Restart your PC. Solution 2: Install the latest FTDI Virtual COM Port Drivers. Download the driver. In the Device Manager, find the entry for the USB serial port (it may have a yellow warning flag), right click, select reinstall drivers, point the installer to the folder containing the FTDI driver you just downloaded. Solution 3 (obscure): Ctrl-Alt-Delete to start the Windows Task Manager. Under the Processes tab, look for HOTSYNC.EXE and end the process. Hotsynch is from a Palm PDA application.
Problem: LED is dim. Solution: Check that pin is declared as on output.
Put the Arduino files into an Application folder. If not, you will get compile errors even for the built-in example programs.
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Symptoms: Cannot upload *and* have checked that Tools > Serial Port matches the COM port number in the Device Manager (see above)
First, pull *all* wires from the black connectors on the Arduino and try uploading. If uploads are OK, than there is a problem, most likely a short in your electronic circuit wiring. If no uploads, go to the steps below.
Try another programming cable and try powering with a battery supply. If green power light does not come on under any condition then remove the microcontroller chip (see below). Reconnect the board. If the power light still does not come on then the board is dead. If the power light does come on, then replace the microcontroller chip (see below).
If the Arduino does appear as a COM port in the Device Manager, then replace the microcontroller chip. Remove the chip (see below) and test with a new chip.
If the Arduino does not appear in the Device Manager, it still may be a bad microcontroller chip. Remove the chip (see below). Connect the board to the computer. If the board still does not appear as a COM port in the Device Manager then the board is dead. If the board does appear as a COM port then replace the microcontroller chip. Remove the chip (see below) and test with a new chip.
Unplug the board and using a small flat-blade screwdriver, carefully work the microntroller chip out of its socket, noting its orientation. To replace, line up all the legs and push gently but firmly into the socket until fully seated. New chips have legs splayed out from a right angle. In this case, before insertion, bend one side all at once until the legs are perpendicular
See ME 2011 Arduino resources page for where to get a new board.
See ME 2011 Robot Store page for getting a new chip.