Suddenly my Arduinoo went invissible

hello,

So I've built and used my Printer for some time now, and one time I needed to check something from the back of the printer and while turning it around, my laptop turned of for some reason, and when i've turned it back on, and tried connecting to the printer on repetier, the arduino would not connect. so i took ir out of the printer, tried plugging to it separately, and it wont show up even on device manager.

So I've switched it out with another arduino mega, that is able to run a blink program, and put everything back together, and the arduino still cant connect, I've noticed in the device manager that the arduino is only visible while the ramps shield is not plugged in.

Does anybody have any Idea what could have happened?
why is the arduino invisible with the ramps stacked on it?
And ay ways to fix this or will I have to buy all new shield and controler?

I have no idea why the ramps board would kill the USB function of the Arduino, unless something on the RAMPS board is shorted and killing power to part of the Arduino board.

I know it doesn't help fix your problem (or maybe it does...), but this sort of stuff is the reason I gave up on Arduino based controllers and computers driving printers via USB long ago. There are just too many ways for things to go wrong. If you end up replacing things, you might want to consider one of the 32 bit boards, and/or printing from SD cards.

USB interfaces in computers don't fail very often. For some reason, Arduino USB interfaces die frequently- maybe PCs have some protective components that are lacking in the Arduino boards, or maybe the grounding is better than in the typical 3D printer.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

It is relativity simple your laptop operating system corrupted the Arduino USB drivers, or a spike kill the laptop USB connector.

Try to load a USB Flash Drive. If this works then the problem lies in the Arduino driver. uninstall then reinstall the Arduino IDE or drivers.

There is a short on the ramps..

If it was a new machine I would say you have the endstops plugged in the wrong way... shorting 5v to gnd..

All you can do is divide and conquer.

remove everything from the ramps that you can. all cables, all pololus.
Now plug the board board into the mega, does it still disappear?
Slowly add things back, one at a time till you find the culprit.

When a laptop USB port gets upset often you need to power down the machine completely, ie un plug and remove the battery and leave it for 30 mins. Often this will revive a dead computer USB (usb chips have some protection)

I found that there's a 200 ohm resistance between ramps Vin and GND, so clearly the reason is there.

I replaced the arduino, before I found that out, and the voltage regulator burned out, but the USB connection works while the ramps is not stacked, the Blink example works fine. everything uploads fine. but when i stack a new healthy ramps (and the USB connection disappears.

reinstalled the drivers and IDE, didn't work

I just now notices that there is a resistance between 5v and gnd on one ramps but not on the other (old one), and when i stack the ramps shield onto an arduino, It doesnt lose the connection. so I,ve started putting things on it one by one and see what causes it to lose the connection ant turns out, the Stepper drivers has a resistance between Vdd and gnd. so I've replaced the drivers with new ones, and resistance on all the new ones are 39,6k ohms. so i figure that all the drivers suddenly burned ( not sure why, they weren't even on when this happened.

now I have everything plugged in to the Arduino exept for the power supply, because I checked again the resistance between the Vin and gnd ( where it previously was 200ohm) and it was gone. gone as in it was the same constantly increasing resistance that you get from capasitors so i checked it on the new Ramps and it was the same..

so i've checked around and turns out that the 200 ohm resistance came from power supply. I thought that maybe my PSU is faulty ( even though it works) and checked around on a bunch of different ATX power supplies and on everyone of those, every voltage rail has a resistance within 500ohm with the gnd. is this normal? or are all of my supplies faulty?

not sure if it is safe to try and plug the supply to the whole thing.