What's wrong with my computer?

[drummerboy]

Whenever I search for something and select the link to the website, it takes me to some strange website that I've never visited. I've ended up having to copy and paste links to get to the page I want. This happens on every browser and even on the different accounts on the computer itself (ie. me, my mom, my brother). Today, I tried to get on Twitter and Tumblr, neither of which were working, and I'm thinking whatever "virus" this is is starting to affect the websites I use. Does anyone know what this is, and how I can fix it?? Thanks!