How to remove a .pif virus from my computer?

Long story short, I was hacked and I was tricked into downloading this file that is going to destroy my computer. It is a .pif file that was downloaded and it is FUD (fully undetectable) so my Norton Virus Scanner doesn't even pick it up. I deleted it from my registry, but I don't know if that is going to do anything. He said once I restart my computer this is when the file will take action. He said it is installed with a RAT (Remote Access Tool). I don't know how to get rid of this file. It is denying my permission to do anything with it. The only thing I can do is move it around on my desktop. It also says it's a MS-DOS Program if that helps you at all. Please help me remove this.