Antivirus kept on poping up hindering others

Hello,
While trying to open an inernet web page, a dialogue box appeared that said "this file has a virus, opening this file may affect your computer". But accidentally I agreed to open the file. After that Antivirus 360 came on my window and asked if I want the threats to be detected, and I thought it was free download antivirus, so I agreed to scan it for me then, another dialogue box came saying the antivirus 360 has detected and started the download process, but to get the full download to scan your computer you have to purchase the antivirus 360. Then this antivirus started to pop up, on all the internet web pages saying down load antivirus 360. Just recently I couldnt open other internet web pages as it will redirect all pages from the web page I wanted to the antivirus down load request page. I dont want to down load the antivirus, onething I dont have the access to buy and dont have the money either. So I wanted this antivirus to stop poping up or redirecting me from the web page I wanted. How can I stop this? please help me as I am usually using the internet for work purposes.