I am having the same issue with the reset button not responding to being pressed.
I am trying to control a fuel injector using the timer2 with a reduced frequency output of approx 30Hz and have a simple 12V buzzer connected to the mosfet IRF5305 output to represent the injector so I can hear the frequency while modifying the pulse width.
Everything was working great last night then I went to try and measure the output signal from the drain using an Oscope and the buzzer went from a pulsing buzz to a steady state tone and then my entire laptop powered down.
I have a diode installed on the terminal block where the PWM signal is coming out of the arduino Uno and connected to the breadboard that I thought would protect this from happening but Electricity isn't my first language. Picture is attached of wiring right before I went to measure the signal coming out of the mosfet.
I think the mosfet is a IRF5305 which is a negative voltage one which took me a while to understand the function and my lack of understanding is probably how I killed the board.
No smoke was released but the laptop shutting down makes me really nervous.
I was connected to the Uno via USB cable in order to monitor the pulse width via serial monitor. I am guessing that the higher voltage from the external 12V battery supply, (with a 5 amp inline fuse), somehow was fed into the DO pin9 and then into the laptop.
Laptop was running on 110V AC power from standard laptop wall charger.
I know that the answer is probably in the code I haven't posted so I need to post the code and will do so in a few hours bc its not on this computer.