If it fails to make the "NEW HARDWARE FOUND" noise under windows.
OR
Does not show up in device manager in windows either as a COM port or other device that needs attention.
AND
You have tried multiple USB cables that are DATA and POWER (they are not all the same).
AND
You have ruled out USB 3.0 issues by using USB 2.0
OR
You have tried it on other computers to see if they can see it.
My issue is that when I plug my board into my computer is that the MKR1000 board will not show up in device manager, the 'on' LED is switched on, I go to the Arduino software and check if I still upload projects to my board. It doesn't work. I tried all the mentioned solutions, I'll make a list :
-The new hardware sound does not come when I plug it in.
-I've tried using three different cables off them are 2 data cables and 1 power cable.
-I only have USB 2.0 on my laptop.
-I tried it on other devices(two, both running windows 10).
-Also I tried to send the CPU into bootloader mode but that didn't show anything
The double tap is timing critical and you could practice that on one of the working boards as you will see when it goes into bootloader mode. in device manager as it will come up with a new COM port.
Other than that you too may have a couple of dead ones.
N.B. To both of you make sure you have nothing else connected to the boards during testing.
Over voltage via any components.
Incorrect wiring.
Placing on a metallic surface when powered.
Careless soldering solder splashes on the board.
Leaving in the anti-static foam whilst powered up.
Over exertion on the board or its components.
The list of things that will let the magic smoke out is as long as your arm and all of them only take a fraction of a second to do the damage.
Well, I am sure there is none from the top 5 you mentioned, besides my MKR1000 is with headers, so soldering is also out.
How can overexertion on the board be defined.
I have read similar post for MKR 1000 not getting detected during a sketch upload due to some error messages..
Is there any hardware based testing to detect the problem with MKR1000?
People have soldered other items in close proximity to Arduinos so just because it had headers doesn't mean its immune to the issue.
I can define over exertion pretty well with a picture of a board that arrived quite recently.
Also people have been known to put too much pressure on the USB connectors and break them off boards or tear the tracks etc.
Others have bent pins or wire leaving parts in the headers that are a PITA to get out.
As far as hardware testing you said you followed all the advice you found so if its not seen by multiple computers with multiple cables and trying the double tap reset trick then there is little else you can try.
If you have access to a well equipped lab and the skills and expertise to chase a schematic around you could go further but that is way beyond the viability of the board.