Lost connection to board

I am using a prusa I3 printer with the acrylic frame. I was moving my y-axis end stop to a new holder i had just printed and i think i accidentally caused a short (yes i know i should have disconnected the power to the printer) because now my computer doesn't recognize the board. My computer doesn't even register that something has been connected to it. when i try to run the arduino file to connect to the printer i get this error message:

Arduino: 1.6.7 (Windows 7), Board: "Arduino/Genuino Mega or Mega 2560, ATmega2560 (Mega 2560)"

Sketch uses 87,342 bytes (34%) of program storage space. Maximum is 253,952 bytes.
Global variables use 3,648 bytes (44%) of dynamic memory, leaving 4,544 bytes for local variables. Maximum is 8,192 bytes.
avrdude: ser_open(): can't open device "\\.\COM3": The system cannot find the file specified.


avrdude: ser_drain(): read error: The handle is invalid.


im still able to supply power to the printer with the usb port, the LED's still work. did i screw up my board or is this fixable?

nevermind its working now for some reason.

ok its still doing something weird. im able to get a connection through the USB but it stops working when i plug in the 12V power supply. i get a message saying "connection lost - a device attached to the system is not functioning"

Just recently went through the same problem
I interchanged some stepper drivers, as one of the motors was troubling me and all of a sudden my board stops working
The light on the arduino is still on. But the red light on the ramps no longer comes up
Any clue on what might be the issue?

i saw another thread where someone did the same thing i did. turns out we broke the voltage regulator. i guess theres a way to work w/o the 12v power supply but im not an expert on electronics. i ended up replacing my boards.