Internet browsers slow, hang, unresponsive?

I need some helP here. Apparently my laptop had a problem with all the major browsers. Im talking bout chrome,safari, and mozilla. Everytime i tried to open a site it took forever to load, and most of the time its unresponsive (noted by kill the page tab by chrome). Its not a connection problem cause im using a wireless router at home and my sister can access the internet fine from the other room. It occured about two days ago and out of nowhere. I remembered that i downloaded some stuff the night before that. Could it be a virus or spyware infection?