Last night, when I browsing some of the page on internet, my antivirus popups and shows virus detect on webpage. I move them in virus vault. That time I am using firefox new beta version and avg antivirus. After some time same popus appear on my monitor screen and pc get shut down automatically. Now when again try to start my pc the virus wouldn’t let me to open programs. i think some spyware infected my pc and can’t able to access my pc. Has anyone else encountered this issue?

Pleases tell now what I can do to remove it?