I can't say for sure because I basically never had such issues, but after reading around a bit, it appears as though quite a few mining viruses cause such behaviour. When opening Task Manager, they hide themselves by quitting and immediately restart after closing it. That also explains the permanent boost clock and power consumption and thus thermals - your system is never really idling. Do you happen to run some games or other software in cracked versions? Because for some time, cracked games apparently came with these mining viruses. I don't know if you can check it there because of the minimal drivers, but does that also happen during Safe Mode?