I am connected via a wireless modem which is connected to a router from upstairs.

Have you reset all the connections and started fresh yet? Meaning did you turn everything off. Then turn modem on and establish connection. Then router then computer?

What OS are you using? Have you added any new programs that take up internet like rss feeds or weather or programs that update on a regular basis ?

I do have a weather program which is probably why. I have just created a network bridge between my wireless and my ethernet, and it has pwned the prob. Apparently from 100 mbps to 400 mbps.