How can I remove ads from my computer screen?

[Amy]

I don't get it. That's all I have to say. Every website I go to is flooded with ads. I don't even know how!! I have a Dell Inspiron 5050 and my mom has some HP laptop and hers is not flooded with ads. We both have the same virus software and all of the same settings, but we don't know what is wrong. I've had the laptop for three months and it has always been like this since the day we bought it. Sometimes when I try to download programs off the internet, it will try to download a totally different program. For example, I tried to download a Minecraft Patch to fix my texture packs and it decided that it wanted to download a movie/video viewer instead. When I tried it again, it downloaded a different viewer by a different company. Is this a virus? Even as I am typing this right now, there are three damn ads on my screen: one for deli meat, another for "Michigan Drivers: Attention: If you drive, read this." (I live in Michigan) and there is another one for "CLICK HERE YOU ARE THE 100,000TH VISITOR TODAY!!". They are really getting on my nerves and similar ones show up on Facebook, Minecraft.net, YouTube, even when I check my email, AND even when I go onto my schools PROTECTED website! Does anyone know what this is and how to fix it? If you can help me I will be so very thankful! Thanks!!