Internet Lag spike Problem

For the past couple months I have been having a pretty annoying issue with my internet connection on my desktop. It will be working fine for a few hours then I will go through a bunch of lag spikes while playing games or even browsing the internet where my connection is horrible but I don't lose it. I am not using wireless and am paying for internet connection that is supposed to be 3mb upload and download. I know it is not a household problem because both of my roommates have no issue with this at all. I have run virus scans and came up with nothing. Right now I am thinking the only option I have is to go out and buy a new version of windows 7 (it came with the current PC I am using so i don't have the installation CD's) and wiping everything on my comp. I wouldn't mind doing that if it solved the problem, I just don't want to waist the money and time with no results. Any ideas or suggestions would be very much appreciated.