I have had this problem two or three times. The following have solved it for me:-
Take Quick Launch out of the Start Menu
Check Resource Monitor. If there is high usage in WmPrve or Svchost there is almost certainly something running in the baskground chewing up memory which can produce a lot of heat. Try suspending them (right click) and see if the usage drops. If the answer is yes you may have some malware in the system but it is much more likely that your drivers are not up to date for the latest edition of your browser.
The last time I had this problem it manifested itself by everything suddenly going ultra slow and CPU usage simultaneously sky-rocketing though nothing large was running. After eliminating viruses, malware, and so no as possible causes I downloaded updates to chipset drivers and the problem went away. I do not understand the technical process but it worked for me.
Avenmarg