Ads pop up out of nowhere and my downloads never work?

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I've been so frustrated with my computer these days. It all happened a few months ago back in 2013 when my computer had to be restarted, because it broke down, so basically what i'm trying to say is that my computer was like a normal computer that could download anything and never EVER had ads popping out. Everything was fine until i had to restart it. Now it's pretty much like the opposite. I tried to delete some things that could've caused it and did many scans. I never really asked anyone since i'm really shy about people looking into my computer. But the problem is that i see ads coming from the sides, bottom, and different places that it squeeze through, but it only happens on different sites. Things i was able to download on my old computer (mmorpgs, etc) never work on here. It ethier suspects it's malicious or dangerous to my computer, and i know those things don't have a virus with them. Some things fail to download and my computers WAY more slower. I don't get whats going on at all, and i just wish one day i could get a new one, but i know i don't have any money for a new one and i just want my computer fixed DX....

Here are some facts about my computer:
I use Google Chrome (i stopped using internet explorer because of tool bars)
I use Windows 3
My computers 4 years old if that even helps ._. ...
Windows 7*