Why is my internet connection extremely slow all of a sudden?

I have high speed DSL, and my current computer is using a wireless connection. A few days ago, it went from being its usual very fast, to dial-up slow. And I have no idea why. I don't have any viruses, my wireless router has a password on it so no one is stealing it, and I have 8GB DDR3 ram in my computer, so that shouldn't be a problem. Help?