Virus on a computer? How?

[▐▀▀▼▀▀▌ ►Levi◄ ▐▄▄▲▄▄▌]

It was night time and my dad let me use his laptop to watch my shows in my bedroom, temporarily because he sleeps in the room I use my computer. This was 3 months ago (during the summer) so I had originally planned to pull an all-nighter.

I only went on the following sites:
http://yahoo.com/ (automatic homepage)
https://twitter.com/
http://chobots.net/forum/
http://www.facebook.com/
and http://www.hulu.com/ (to watch my shows)

^I've been on all of these sites, hundreds of times, and never received a virus. I've also made it clear to my dad (and I'm pretty sure he checked the internet history). But the next day when my dad used it, he told me he couldn't access the internet. Today, the guy at Office Depot told him he gotten a virus. My dad then started assuming if I did something or downloaded anything because he couldn't determine what kind of virus was we got.

I tried looking at the internet on there a few minutes ago, and when I clicked, the Internet Explorer icon, it should just show a loading window saying "(Not Responding)." My dad thinks the internet has been blocked.

If it helps, the laptop he's using is a Windows and the internet is Internet Explorer. We had a Norton Firewall. I also did not download anything nor visit any site other than what's listed above in the 3 hours I used the computer.