Why are these ads appearing, and how do I get rid of them?

I've been using Google chrome for a while now, and nothing like this ever happened before, but now these ads keep on appearing. For some reason, there are these games, and they gust pop up when you click on the text box on Google. If you accidentally click it or play the game, it redirects you to some website, which is Asda's homepage most of the time. When i have managed to search what I wanted, it comes up like normal, then, after a second or so, some ads appear at the top of the page. There are 'web cake' ads which aren't as bad, then ads that are trying to look like windows security alerts (e.g. Your computer is at risk. Click fix it to repair the problem) and underneath it says 'ads not by this site' so how do i get them to go? I've looked on my google settings but thats no help as the ads aren't google's fault.

Oh, and sometimes, when i enter a website, such as yahoo answers, it comes up with all the graphics gone, and just text. Why is this happening?

Please help, this is sooooooo annoying!