High CPU Usage

Hi.

I have a problem with my laptop since yesterday. Something invisible is using very high cpu usage. I said invisible because it didn't show in task manager and process explorer.

It all comes when I was browsing some pictures in Google and downloading YouTube videos using IDM. Everythings runs fine but when the downloads comes to about 60%, my laptop fan starts to getting loud and lagging cursor movement. Opened task manager but the cpu usage says 11% (even it is stuck at 11%). But my desktop rainmeter showed that my cpu usage is 100%.

I tried restarting, it works. This time, rainmeter and task manager shows only about 10-20% cpu usage, but my laptop is still slow. Didn't slow like before, but I noticed that my framerate in some games dropped significantly and the fan is loud. It means that cpu usage is still high, but task manager, rainmeter, and even process explorer didn't detect a program that has high cpu.

Can someone help me?
Thanks.

You have a laptop designed to run windows 7/8.1 and you are running windows 10 on. So you have no driver support for windows 10.

You might have picked up some malware from the YouTube videos or the pictures.

I would scan the laptop with a good quality anti-malware program like MalwareBytes and see if anything shows up.