PC frequently freezes, restarts when booting up game. Event Viewer shows Kernel Power 41

The problem has been persisting for 2 weeks now and it’s driving me crazy. Whenever I boot up and play a game that puts up heavy load on GPU (100% usage) for 5-10 minutes, the PC just freezes for around 2-3 seconds, then the screen goes black (monitor loses connection) but case fans and CPU cooler are still running. 10 seconds later the computer restarts as if nothing has happened. When I check Event Viewer it shows source is Kernel Power – ID 41. The BugcheckCode is varied, sometimes it’s 159 but mostly 126. The problem also appears occasionally when browsing web and doing stuff that don’t rely on CPU and CPU power but that’s just minor. My PC build is

• i5 9400F running at 3.9Ghz max load
• 16Gb Crucial Ballistix Sport 2666Mhz
• Aorus B365M Elite
• Gigabyte GTX 1660 Ti running at stock clock
• Cooler Master MWE500 White v2

I built it about 10 months ago with all hardware brand-new. Before the problem happened, CPU had been running at 75c and CPU at 70 at full load so heat shouldn’t be the problem. What could possibly be the culprit?

Thanks.