Virus on my PC

Hello,

I was streaming a movie online and a box appeared saying that there has been a virus intalled on my PC. Now al that happens is this box keeps popping up saying "application can not be executed. The file (and it varies) is infected. Do you want to activate you Antivirus software". When I click yes it scans and has found 34 virus threats. All it does after is send me to AntiVirus Live and ask me to order the software to erase the threats...Is there any other way then ordering the software it ask me to buy. What would you recommend to get ride of the viruses