Having this nightmarish problem!!

[1nv1ctu5]

I am having these weird reboots while playing games. Sometimes I can play for hours without any issue arising. Sometimes i get BSODS,but these are very very very infrequent. I have an old system, which I was gonna change but then this pandemic happened and the price of components just skyrocketed. So coming to the point, when the system reboots without any warning and boots backup, my keyboard and mouse become absolutely worthless. They don't work at all(both of them are usb). I change ports  i change keyboards and mouse, nothing changes. I have to shut down system directly from my Cabinet's power button. I thought it was maybe some faulty ram (Corsair valueselect 16gb 1600mhz) that is causing these issues so i removed 2x4gb stick and tested them, then i put the 2x4gb sticks, still happened. Is it motherboard( Gigabyte ga-78lmt-s2pv), or my PSU(Cooler Master MWE 650 Bronze V2 230v, 80 Plus Bronze Certified, Non-Modular Power Supply) is the culprit. I am completely stumped. any input is appreciated.