My computer is claiming it is infected with a "blaster worm".?

I've tried to get rid of it by downloading soft wares softwares,(i.e. fix blast, sophos, mcaffee) but none of it will work. Right before i click start it completely goes away and then my computer says that the software was infected by the blaster worm. My computer claims that it's a W32/Blaster.worm. Help, please!