Completely random CPU usage

Hello, I registered to these forums as I need help with the problem I encountered with my PC.

Some time after startup ( Not right away ) my CPU usage goes to 100%. I open task manager and kill the process which takes most of the CPU and then another process gets the high usage and so on untill some system process which I am afraid to kill or some app that I need gets it.

Problem started happening a while ago, I thought it's just a problem with my OS which collected garbage over the time as I didn't really keep it clean. Few days ago I reinstalled my OS and this thing is still happening and I really have no clue on what it is or how to fix it.

I provided a screenshot of resource monitor below, it shows that resmon itself uses 24% of the CPU which I find quite weird.

Note: System is updated with the latest updates from windows update. I also have AVAST Premier and I run a boot scan 2 days ago and it didn't detect any virus.

I took a look into my PC's temperatures and it said CPU is at 80+ degrees. I changed the pasta thingy, cleaned it from dust and added a new cooler to my GPU ( GPU wasn't really over-heating, but summer is coming and stuff will become even hotter ) and it seems to solve the problem.

Now, I am having a hard time understanding how can temperature cause things that I said above.

The probable reason for those results is the way resource monitor calculates CPU usage. When you were running hot you were probably throttling and your CPU run at reduced maximum frequency, let's say for example 1GHz. So any time there was higher load requiring your CPU running at 1GHz monitor would show 100% utilization at that particular moment, since it knew your CPU can't run any faster. After cleaning, your CPU runs cool and can go to lets say it's real max 2GHz, so now with the same load as before requiring CPU again running at 1GHz to perform all tasks, the monitor will show 50% cpu utilization at that particular snapshot, since it still has headroom to go 2X as fast. Hope this is clear.

Ok, thank you very much for that explanation.