Why Is My Computer Running Slow

I’ve tried Avira, but that just has an endless array of pop ups urging me to upgrade to the paid version. I’ve also used Avast and that usually makes my computer slow to a near halt when it updates itself. Is there such thing as what I am looking for?

My computer is running really really slow today.No matter what site i try to go to after a few mins it comes up navigation problem refresh this page.It wont even let me retrieve my mail. Whats the problem