- Does that straight forward code make use of pins 0 and 1 (anything connected to them)?
- Anything else connected to the board?
- What is the serial-to-usb converter on your board (the chip closest to the USB port)? If it's not the CH340 (used on most clones), you can run the loopback test and report the results here.
- What happens when you press and release the reset button; do you get a few short flashes?
- Which board? The baud rate indicates a board with Optiboot (Uno or new Nano). If it's a Nano, try the different option under tools → processor.
- Does COM 3 disappear from the list of boards when you disconnect the board?