Arduino Mega 2560 disappeared from device manager

Using Arduino IDE 1.x
1

Hello,

I bought an arduino mega (no clone) this week and was surprised how smooth everything worked. Had it installed and a couple of tiny projects running within a couple of hours.
Today I wanted to continue to explore some shift register shenanigans which I need for my next idea.

The problem now is:
The Arduino simply disappeared. It is not longer listed on the serial ports in the IDE, nor in the device manager. (Note that it is not listed as an unknown device. It is completely gone) I tried a variety of different USB cables and ports, hit the RESET button like a madman, re-installed the arduino software (using the windows7 installer 1.0.5 r2) and did a legacy install of the mega2560 (including R3). All with no cigar.
Also rebooting my system does not help.
I want to perform a loop back test, but I am not sure which reset-pin I am supposed to set to ground. (There are two pins which say reset, one by the reset-button and the other close to the 5V power pin). So I have not tried that yet.

When I connect it via USB the green ON light is running continuously and the orangeish LED next to pin 13 blinks once and then stays on. (In some cases the orange led blinks once and then stays off, if I unplug the USB and replug it again, it usually stays on).

Some help would be much appreciated and also some articles, which are a recommended, to read to understand the USB communication process.

I am pretty much a novice on this field, so in case one of you can suggest me anything: please pretend that you are talking to a child (even though I am a grown physicist :cold_sweat: )
I used the search function, but nothing could really answer my question properly. So if I overlooked a thread in which the answer to this problem has already been posted, I am sorry and will walk in shame.

Thanks for reading!
Cheers!

edit:
Maybe some additional useful information: During the days of operation, it happened that it disappeared every once in a while, but replugging made it comeback every time.

tl, dr:
Arduino Mega 2560 worked fine for a couple of days and now disappeared from my system. what do?

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Thanks for you input, but I already tried different usb cables/ports. I even tested it on another machine.
The only device which is listed in the COM section is something called communication connection (or similar, I have a german OS, Kommunikationsanschluss)
Anyway it is not the Arduino. After some research I stumbled upon the 16u2 chip which occasionally fries. I will try to flash it next week and keep the thread posted.

Cheerio

4

So I just flashed my atmega16u2 using an avr mkii.
The flashing process went smooth and the arduino appeared again for a short moment, only to throw an error, while windows7 tried to install the driver and then was gone again...

the atmega2560 on the arduino works fine. i could program it via mkII.