pc reboot

recently my pc is behaving super wired. pc getting restarted suddenly when i start pubg pc. on other games like rdr2 and other heavy games, when starting any game and after 10 mins pc suddenly gets restarted. i have tried multiple troubleshooting steps like reinstalling graphic driver, rollback...

The computer has been running fine for the past 2 years, and normally does not have any problems running without ethernet (or if cable is plugged in before booting up the PC). This issue started occurring randomly when a whining noise started being heard in headphones. Reinstalling realtek...

Something I noticed lately that my PC boots the moment I press the spacebar in my keyboard. Initially I thought I did not shut down the PC, but later figured out even after a proper shutdown it boots just by hitting the spacebar. Recently I updated my BIOS, is this anything related to BIOS...