Your Internet Browser should have, under tools or preferences, a place to block unwanted sites. Sometimes you have to blocked a site. You can use Internet Security programs to help.
Browsers like Mozilla Firefox and Google Chrome are very good at blocking pop-ups. If using one of those does not fix it, it is likely that your computer is infected with malware. Use a good free anti-malware such as Malwarebytes or Super Anti-Spyware. Get a good antivirus program like MSE.
