Discconnects after a second of load (fan, stepper, anything)

I have a mega2560 with ramps board for my prusa I3 rework. my board is acting real weird now, it was working before - then i went to adjust a pot on a stepper driver when it was on (stupid i know) and the screwdriver slipped and I hit some contacts. I got the widnows 7 x64 usb disconnect sound. Now the only way I get communication is when I plug in the USB first (before I could do power first, or usb first). Then when I plug it in it shows up in device manager and connects in Repetier and shows thermistor temp as room temp and moves around a a bit so i know its communicating. Then I can run any one stepper for about half a second or a fan for about 5 seconds then I get the windows usb disconnected sound and no more communication.

Is this perhaps a voltage regulator? I tried removing all stepper drivers and wires, everything but the fan, didnt help.. i tried removing everything but one stepper driver and one stepper motor, same results. I even tried a new power supply.

any help you can offer would be great. thank you

then once it disconnects I can unplug it and plug it back in and i get usb device not recognized until I remove the power supply then plug the usb back in. this is so weird.

I found and fixed the issue. I will post here to help anyone who has this issue in the future.

The problem for me was the R2 diode. It was feeding my sending to much power to the ardunio from the 12V power for the steppers and heaters. I removed it (now it needs usb power with this removed, or I can replace it) and it works perfect. No more disconnects.

I found this by powering the stepper with less voltage and it worked, as soon as I upped to to 12 and ran a stepper fast it overloaded.

This most likely means you've blown the on-board regulator on your Arduino Mega2560.

A simple way to test is try running the Arduino (without the RAMPS board) using the DC barrel socket. I suspect that it will fail in the same way.

As you found, if you remove the D2 Diode and then power the board via USB, it works for you. You won't be able to use the printer stand-alone unless you use a USB charger to run the Mega2560, or replace the Mega2560.

Note: Sometimes the regulator fails in weird ways, so in some way you're lucky that it's working fine via USB. Some people haven't been so lucky.