What can i download for free off the internet to get a virus off my netbook?

the other day a pop-up screen came up on my netbook and it was connected to the internet but i wasnt sittin at it and when i sat down that pop-up screen had jus downloaded and a anti-virus software to my computer. but it is actually a virus, its called "Antivir Solution Pro" and its taken over my computer, it wont let me open the add/remove programs option on my computer something pops up and says its infected,the majority of the things i clock on that i have installed on my computer it wont open now because that screen comes up and says that its infected, i tried to get the AVG anti-virus earlier and it let me save it to my computer but wouldnt let me open and run the program because that "Antivir Solution Pro" says its infected.my original anti-virus was McAfee and it expired a few months back and i never renewed it,this new "Antivir Solution Pro" says its a demo version and the removal option has been disabled and it doesnt say how long the demo version is.it will also make websites come up like for viarga and adult websites which have never been looked at on this comuter so i know it has to be a virus. ive also did a search for the name of the program on my computer and it doesnt show up. so is there a way to get this off or do i need to take it somewhere and get it fixed?! i go to school online and it starts in couple weeks so i need it fixed soon! any feedback will help!