The board is not detected on the serial port and the upload fails to connect — where do I start?

For step 3 specifically, since it is where most people are stuck: identify the chip before hunting a driver.

Look at the small chip near the USB connector on the board, or at the device description Windows shows. Common families each have their own driver and they are not interchangeable. Buying an inexpensive clone board very often means one of the third-party bridge chips rather than the one on the official design, and it is why the official instructions do not match what you see.

Two warnings that save an afternoon:

• Get the driver from the chip maker or the board vendor, not from a search result offering a bundled installer. This category of download is a favourite of bundlers.
• A previously installed bad driver blocks the good one. If an earlier attempt left something broken, uninstall the device and tick the option to remove the driver software, then replug.

If the port exists and the upload still fails with no serial data received, the usual causes are:

• Something else holding the port. A serial monitor left open, another editor, a logging tool. Only one program can have it. Close everything and retry — this is astonishingly common.
• The board is not in a state to accept a program. Some boards need a button held during upload, or a specific reset sequence, particularly the wireless families. The documentation for your exact board will say; the generic instructions will not.
• A sketch that immediately reconfigures the pins or crashes can make the board unavailable moments after reset. The recovery is the manual bootloader entry above.
• Power. A board drawing more than the port supplies browns out mid-upload. Try a powered hub or a different machine.

Test the chain in order, because each link produces a different symptom and the fixes are unrelated.

1. Is it a data cable? This is the single most common cause and the most infuriating. A large fraction of USB cables sold with devices are charge-only — power and no data lines. The board lights up, so it looks alive, and the computer never sees it. Try a cable you know carries data before anything else.

2. Does the operating system see a device at all? Look in device manager with the board plugged and unplugged. If nothing appears or disappears, it is cable, port or board power. If something appears with a warning marker, it is a driver.

3. Is there a driver for the USB-to-serial chip? Many boards use a third-party bridge chip rather than native USB, and Windows does not always ship a driver. This is what produces the port simply not existing. Install the driver for the specific chip on your board.

4. Does a port appear, and is the right one selected? Ports get renumbered between plugs.

5. Does upload succeed? Only now is it about timing, bootloaders and settings.

One diagnostic that separates hardware from software in ten seconds: plug the board into a phone charger.

If it powers up and runs whatever was last on it, the board and the cable's power lines are fine, and you are looking at data lines, drivers or software. If it does nothing, it is power or the board.

Same idea with a second computer. Two machines behaving identically points at the board or the cable; different behaviour points at the machine.