Overheating of Arduino board (mega) and laptop shutting down suddenly

Hi everyone, I am posting on behalf of a young friend who needs urgent help. I am not known to this, but any help is appreciated.

So my friend was making a small project 3D printer using Arduino (Mega). He is using an external power supply (12V SMPS) for powering the circuit. When he tested the printer's motor, by connecting it through the USB port and commanding through his laptop, everything was fine.
However, the moment he tries to test run the DVD drives with 2 stepper motors, the board gets hot beyond touch and smells burnt for some reason. This is not all; the moment he connects the board to the laptop, it force shuts down.

I am not that good with technical stuff but I think there's some kind of excess current through the board that is heating it up and causing the laptop to protect itself by abruptly shutting down.

I am sharing the YouTube link to the video he has been using as his guide below.

Any idea on what this issue is and how can it be resolved?

There are some very clever people in this forum... that is true.

But... they are are all completely clueless without information... you have provided very little information... so I fear you will not get the help you need.

Maybe a schematic of how your components are connected will give them something they can work with... is that possible?

The Arduino runs on 5 V, not 12 V.

No idea what the stepper motors require, but they would require a proper drive circuit.

Unless you provide some information on what the system is question is built from, we have no idea how many things are wrong! :astonished:

This is what he has been following. I asked him to send me any schematic he has.

Yes yes..
I will try to collect as much specific information i can. Thank you for your response. Much appreciated

Sounds very like CMOS latch-up - this means something is putting a wrong voltage onto one of the Mega's pins, causing large currents to flow and triggering CMOS latch-up. You must prevent this from happening, its very likely to fry the chip completely. Its essential to cut power immediately if it does happen.