Why is my Ping fluctuating up and down?

I'm playing Counterstrike Source, and my Ping is usually around 30 - 70, but tonight its been going from 125 - 900, sometimes even going above 1000 for a moment. I keep getting kicked because of this and I'm getting pissed off. I moved downstairs right next to my router, but the problem still persists. I thought maybe people were downloading, and I saw my dad was seeding 10 downloads on his computer, so I removed them and turned off every other computer/laptop in the house. Nothing seems to be working. I even ran a virus check but my laptop's clean. I just did a speed test and the first one my ping was 16, and the second time it was 210. Any suggestions?

mine was jumping for 600 to 70 this whole weekend. turned out its cause when i installed my new sound system i must have moved my computer to far backwards were all the clutter was . i moved my computer forward now im bakc to getting 50 ping. if u have a wirless connection just move ur computer abit and see if that helps