Sometimes, you may have problems accessing certain sites and not others. If you do then try this:
https://www.whatsmydns.net/flush-dns.html (https://www.whatsmydns.net/flush-dns.html)
You can also start the command promt (or any other program) in administrator mode by typing it in the search box. For instance, typing cmd and pressing Enter will open the command prompt. BUT, instead of pressing Enter to open it press CTRL, SHIFT, + ENTER to open it in administrator mode instead of regular mode. ;)
I do this for the heck of it a few times a year or whenever I start having problems accessing certain sites and not others.