|I was just having the same problem right now.|
After scaning to see if i had viruses, I took a look at the setings of the antivirus and saw that Advanced Disinfection was turn on.
Computer went back to normal after I turn that feature off and turn on concede resoursces to other applications.
(It's in setings, compatibility).
My guess is that some lates update must have turned Adv.dis. on as I don't recalll turning it on as there is a warning that it can slow down sys performance.