Kind of strange. I have a Gigabyte X470 Aorus Ultra Gaming motherboard. I had a Ryzen 5 2600 CPU, but I just got a used Ryzen 9 3600X off of eBay. My BIOS is up to date, and I have verified that the version of BIOS I have supports the Ryzen 9 3600X. After swapping the CPU, the computer boots fine, but if I log into Windows 11, after about 1-2 minutes the system will reboot/reset. If I do not log into Windows, and instead just have it sit at the lock screen, or if I boot into the BIOS, it can sit there forever without rebooting. It is only after I log into Windows that it reboots. I thought maybe my power supply might not be enough for the more powerful CPU, since I had a 430W power supply. I have an older Nvidia GTX 1050 video card, so nothing too crazy. I replaced the power supply with a new 750W Gold power supply and I have the same problem.
I am not doing any overclocking in the BIOS. I have reset the BIOS to use optimized settings.
I hate to reinstall Windows 11 to see if the OS does not like something between the changing of the CPUs. Seems like it should be able to handle that. I am thinking about maybe making a bootable USB thumb drive with Windows on it, and booting from that and see if it is OK with that to rule out Windows.
I am about to send the CPU back, but thought I would check and see if anyone had any other ideas as to what it could be...