How to remove windows xp recovery fake alert!!!!?

I've got this virus and its taken over my computer, none of my programs are visible, can't even get on the internet, my screen is either blue or black, i have mcafee and webroot, ran the scan twice, both times webroot found it, but its still there, can someone help me remove it in laymens terms, so that i can understand it, i unpluged from the internet and ran a full scan also.......... Help, Help, Help!! and i can't afford to pay to have it done i.e. best buy geek squad ect!!!