Processor speed limited at 0.4 GHz

I suggest you check your CPU fan: maybe it died and the chipset is smart enough to detect it and throttle down the CPU, but not smart enough to tell you what the problem is.

If you have recently changed power adapter, it might not be providing enough power for the CPU to ramp up, which could cause the throttling you're experiencing.

That was at least the case for me last time I experienced these symptoms.

From everyone's feedback I questioned my hardware, and my fan more specifically, and that was indeed the problem. What I've done was pretty simple "have you tried turning it off and on again" hardware manipulation: I've opened the laptop, unplugged the fan, turned it on for some seconds, turned it off, plugged the fan again, and it was spinning. I've also moved manually the fan before that when it was still turned off, just in case it was stuck for some reason. Don't know what did the trick, but it worked, and yes the motherboard was detecting the fan issue and throttling the cpu, as now it's working perfectly even without the fan spinning on low load work. Thanks for all the suggestions, as this issue has risen after I've played with the power options CPU limitations, I thought it might've been a software thing, and maybe that played a role, who knows. Bottom line, this worked for me, hope it works for others as well!