i5 9400f posts only on 1 core - multicore results in watchdog error

[Alex_CPU]

I've got a HP Pavilion 590-p0063 with i5 9400f, gt 1030, single DDR4 stick, 16gb optane+hdd. Latest BIOS now. 

PC fails to post on default BIOS settings - was giving me a watchdog error. Linux gave me soft lockup - CPU cores stuck for XX seconds.

I've disabled multicore and it posts on 1 core, was able to install windows 10 and linux and no issues.

After fresh windows 10 and drivers, enabled multicore in bios - PC posts but I get 100% CPU utilization and enormous speeds - 0.5Mhz to 500000000GHZ - it is just all over the place. Thermals and noise seem fine. 

System not stable at all, tried running userbenchmark but failed straight after HDD check. 

Just to clear this, PC was working fine for 1+ years. No damage, no leaks. I've cleaned the pc and internals, checked CPU socket, checked CPU, tried different RAM in single and both channels. Tried HDD+Optane, tried m.2 nvme. Tried another GPU and still same result. 

Is this a bad CPU then? or the motherboard? anyone had this issue? 

[Prométhée]

hi

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