My computer, and indeed anything WiFi or Internet-dependant, became sluggish in the last few weeks.
I had assumed that MS or some Government was examining all my jpg files for wickedness.
SO we had an extended power outage, 12 hours, and on switching everything back on, every device absolutely snapped to life!
They do recommend rebooting the router every so often, and I do believe I had done.
But clearly, totally de-powering EVERYTHING seems to have had a major effect.
Do try it...