need to isolate fried component

I accidentally shorted the +5v terminal with the GND terminal in the AUX-1 section of my RAMPS 1.4 board. I really wish I hadn't done that.

Now Pronterface can't connect to the board and gives this error message:

[ERROR] Could not connect to COM1 at baudrate 250000:
Serial error: could not open port COM1: [Error 5] Access is denied.

I assume I have fried something on the RAMPS board or the Arduino board but I don't know how to figure out which component. The RAMPS board is still somewhat alive: when I press the reset button the green LED flashes twice. Also, the extruder fan still runs fine - it's still getting 5v. And the RAMPS board is still getting 12v power from both of its connections to the PSU.

I suppose it's possible I fried the COM1 port on my PC but I don't know how to check that either.

How do people who know stuff (clearly not me!) isolate problems like this? Thanks!

Most likely you burned out the 5v regulator on the Mega.

Thanks for the tip! But if the 5v regulator is toast, why I am still seeing 5v on those pins (and powering the extruder fan)?

Yippee, it's working again and the problem was hidden in plain sight: Pronterface was attempting to connect to COM1 instead of COM3. I'm guessing that when I shorted out the +5v and GND connection, I was shorting out the power coming in from my PC via the USB connection. That caused the PC's COM port to reset or something and Pronterface reverted to the default port, COM1. Anyhow, all is well in Pepperland again!