Why is my laptop suddenly shutting down?

Hi everybody. I am using a Dell precision 7520 laptop, everything was working normally until about a month ago, when suddenly my laptop suddenly shut down. I took it to the repair shop but the mechanic couldn't find the cause. That incident doesn't happen on a cyclical basis at all. Sometimes I open youtube in about 7 or 8 google chrome tabs and leave it not touching anything, the whole 5 or 6 hours the laptop is not damaged at all. Sometimes when I open youtube and just touch the keyboard or touchpad, it suddenly shuts down. Until today the laptop could not boot. I press the power button, it lights up, the screen shows the Dell logo and the keyboard light also comes on, but right after that, the Dell logo disappears and the keyboard light fades to completely off, the power indicator light blinks from green to yellow and then the heatsink fan hums and then shuts off. Please help me diagnose what is wrong with my laptop. Its model is intel core i7-7820HQ, 32GB ram, 256GB Samsung NVME ssd, M2200M VGA. Thank you everyone for reading.