If the hardware is OK, as you say, it's a software issue.
Then the easy and guaranteed solution is to go back to factory conditions (or a reset in Windows 10), then go forward with all Windows updates, reinstalling your applications and restoring your data from your backup.
It takes some time, but finding the culprit night take a long time also.
Am having an issue with my operating system when I try to run any application. When I watch video on my computer it freezes for like 2sec and resumes, when I open an application it stops for like 3secs then it opens, if it's a program say Corel Draw or photoshop or any other, whiles on the program it freezes for like 4 to 7sec when using a tool. Am running on an i7, 8GRam, I have run diagnostic on the hard drive and memory everything is working perfectly. Can anyone here help with this issue