High CPU usage, computer gets hot, slow browser

[tilman_berlin]

Hi!
Yesterday this problem suddenly occured: my computer got slow, internet browser (Firefox) works very slowly, the fan is always running and the computer got hot (I usually only see my computer getting hot when I use programs that need high performance: video editors etc.)
I checked the CPU usage which is constantly very high. I ran Malwarebytes and Avast which found nothing and did not change anything. I deleted all temp files, rebooted several times, still no change.

You can see the details about my system in the screenshot. The machine that I use is a Lenovo Thinkpad, Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz   2.59 Ghz, 8,00 GB RAM

Can anyone help me with this? I don't know how to go on.

Thanks very much

Tilman

[tilman_berlin]

Additional information: the cpu usage drops to normal when I deactivate my wifi connection.

[patio]

What size HDD and how much free space ? ?
Also ever had the fans cleaned at a shop ? ?

[tilman_berlin]

Hi Patio,
the HDD has 222 GB, 11,7 GB are free.
The fan has never had a cleaning so far. Interestingly, when I disconnect from internet all the problems disappear, including the overheating and the running fan.

[SuperDave]

You can check your fan speeds and also your computer's temperatures by downloading and running Speedfan

Windows requires at least 15% (33 Gb) of free space to operate. You will need to free up some space. You can do this by removing/uninstalling no longer used or unwanted programs. You can also transfer important documents, photos, music and videos to an external harddrive or DVD's.
I would also advise you to uninstall Avast if it is the free version and just use Windows Defender.