Computer Problem! Virus!!!?

I was on some forum site I'd never been on (I googled something and it came up) suddenly my laptop shut down. I thought it was dead or something, but it was on the charger. So I turned it on and tried to get back to where I was but i got four popups from Win 7 Home Security, saying I have infections (virus like Trojan), my anti virus needs renewed, so i decided to do that since I have no idea what Win 7 is, but it won't let me on the internet! Like a popup comes up and says, "This is not safe," and exits the site