Antivirus Soft

What a headache do I have! My other computer got infected with Antivirus
Soft, I believe it is malware. The problem is that it will not let me browse
the internet to download Malwarebite's Antimalware, which I read in a post
that will take care of it, it really does not let me browse for anything! it
keeps going to and will not even let me do a system
restore, that PC is running XP Home PLEASE HEEEEEEEEELP!!!!!!!!!!