Can't upload to ArduinoMicro - bootloader 'COM6' briefly when plugged in via USB

In Windows 8.1.

I was able to upload, both from Windows and from a RPi but now I can't - not sure what's happened. I'm now trying to upload from Windows 8.1.

Back when I was able to upload from Windows, connecting the Arduino would trigger the 'new USB device' sound, then the 'USB disconnected' sound would play, followed by the 'new USB device' sound. I think this is something to do with how the Arduino micro interfaces via USB either as a bootloader, or as the running Arduino (no clear idea what exactly is going on).

Anyway, now this is what happens:
Plug in Arduino Micro.
USB connected sound plays. "Arduino micro bootloader (COM6)" appears briefly in Device Manager.
USB disconnected sound plays. No sign of Arduino.

After that, there's no COM port visible in device manager, so no port can be selected in Arduino IDE.

I attempted resetting the Arduino 'during upload' to see if this would make uploading work. However it leads to Arduino IDE sitting forever 'Uploading' to no avail.

Any ideas how to fix my Arduino Micro?

Hmm - from the Troubleshooting Guide:

Bootloader
Make sure there's a bootloader burned on your Arduino board. To check, reset the board. The built-in L LED (which is connected to pin 13) should blink. If it doesn't, there may not be a bootloader on your board.

I see no blinking LED any more. No bootloader? Not sure how that could have happened.

Thanks
Innes

Where did you get the board from? Have you got a link?

I bought this Arduino Micro from Maplin. Now I'm thinking the lack of a flashing LED doesn't mean no bootloader - it's because the sketch I uploaded just doesn't flash that pin. Initially everything worked on Windows. Then I tried using with a RPi and that worked, but then upload stopped working. Now back on Windows it still doesn't work.

I found these instructions for timing a reset of the Arduino Micro when Arduino Micro fails to auto-reset the board to initiate uploading. Maybe I was timing things wrong when I tried this before:

These differences affect the way you use the physical reset button to perform an upload if the auto-reset isn't working. Press and hold the reset button on the Leonardo or Micro, then hit the upload button in the Arduino software. Only release the reset button after you see the message "Uploading..." appear in the software's status bar. When you do so, the bootloader will start, creating a new virtual (CDC) serial port on the computer. The software will see that port appear and perform the upload using it. Again, this is only necessary if the normal upload process (i.e. just pressing the uploading button) doesn't work. (Note that the auto-reset is initiated when the computer opens the serial port at 1200 baud and then closes it; this won't work if something interferes with the board's USB communication - e.g. disabling interrupts.)

Does the last sketch you uploaded use serial? It is possible that it is hogging it so what you would do, is hold down the reset button and release just as a sketch is uploading.

Yes that must have been the problem. I got the blink example sketch uploaded fine doing that.

I am pleased it's fixed. People do that all the time....