explorer.exe uses 100% CPU

My computer's been full of viruses lately. And now when I try to start up the computer, the explorer.exe uses up 100% CPU and my computer goes extremely slow. What am I supposed to do to stop this?

Also, what's the best good and free virus scanner/removers?

Dear asshole who likes Vista:

I hope you die. You had to stand there while I packed up my groceries and chatted happily with the cashier because I'd bought good food---even cheap meat is good when you guy fresh spices to go with it. I"m sure you think that you're somehow entitled to steal anything you can find because somehow you've been wronged. But consider this: this is who I am. You have just deprived me of one of my two methods of installing my own software, and my only method of downloading free music. I can feel the blackness sweeping in on me, a depression that a year of war somehow doesn't equal. In war people want to kill you. Evdiently your fellow citizens just want to screw you. I wonder if I were a young guy with muscles, a high-and-tight haircut, and the obvious look of a veteran if you'd have stolen their fair-use rights.

I hope you die. I have no way of consuming media without paying, or of beating off to loli-pron. That's what you did to me. That  operating system represented 1/2 of my yearly income and was a necessity. I had it exactly thirty days. You'll probably pop he activation key and use it to boast to all your shitty friends about the free OS license you scored. I paid for that key, and I hope karma tears you to shreds.

If anybody offers sympathy, I will scream. I want revenge. I want trial by combat. Oh, and by the way, Cub Foods? Tahnks for being so not helpful. There are assholes who steal, and then there are assholes who just shouldn't work with the public. Thanks bunches. I'll take it to corporate if I have to. I hate you.