Like the title says: the computer is running like it is on steroids.
I have been searching for the problem, but I cannot find it.

htop and top don't give any weird feedback. My browser takes 10% Memory. But that is the only process that takes a significant amount of memory.

What tests to run to determine what causes my computer's fan to work like crazy.

when was the last time you removed the DUST!!! from inside ?

and from your 3d card

the fan cover on the card heat exchanger is a TRAP for dust

2 members found this post helpful.

Lol! A long time ago. I will look into it. Thanks for your answer.

The first and most obvious thing to ask in any such situation is: What has changed recently? Were there any patches/updates applied? System rebooted? New hardware added?? SOMETHING has to happen to cause something to change...that's the best place to start. Also, you really need to provide details when asking questions; things such as version/distro of Linux, what kind of hardware, etc.

Aside from general dust, APCI is typically the culprit...but again, if it WAS ok and now it's not, what changed?

Seems your CPU/GPU too hot.
Install and configure lm-sensors. it shows how hot is your CPU/GPU and how fast fan rotates.
As well you can check your BIOS for temperature and fan RPM.

JohnVV's suggestion is my top one. We fortunately have a machine shop and an air hose, which I find useful to blow high pressure air at boards and assemblies to flush the dust out. And you do have to pay attention a bit to the destination, just in case you may be flushing towards compression internally versus "out" . Either case, that's a thing I'd recommend is to try to get dust out of the system first and see if this was your problem.

That may be an indication that your motherboard is going bye-bye -- you turn it on and the fan goes full blast that may be a bad or leaky capacitor on the board.

Only know that because one of my old boxes (a Dell Dimension 8600) exhibited exactly that. Got a replacement motherboard for $50 on E-Bay, swapped it in, life is good.

Of course if there are two inches of dust bunnies and dog hair inside... well, that could be it too. Get out the vacuum, the compressed air and stand back (outside is good here).

Hope this helps some.

If you got a compressor set it about 20-25PSI and give it a Good Blow Job. Make sure you hit the power supply also.

If there's a process taking up most of your CPU capacity, kill it.

EDIT: Oh, you already tried that. Never mind.

Layers and layers of dust. Literally, cakes of dust. It is that I cleansed it by TL light but otherwise I would have taken a picture of it.
I knew of course that there was some dust in the computer but I didn't know that is was THAT BAD!

Thank you for your answers.

the simplest things are normally the FIRST thing to look for