Please help! I think have Adware on my computer? how to remove it? Windows 8.1?

[Kiara]

I have no idea how to get rid of it, its only on certain pages too, how ever the ads are always similar, and in the same positions. like "FACEBOOK HIRING"
._. its getting real annoying, and I'm concerned it might end up hurting my computer, even if it doesnt, its bloody annoying e_e

I have windows 8.1 so im not really familiar with it either. I thought maybe windows defender might help, but it keeps saying this app has been turned off and isnt monitoring your computer.
Honestly this is getting really annoying since the lay out is just so much more complicated and complex than windows 7.
I have nortons internet security(trial) And i always scan my computer and the most it comes up is with tracking cookies. I'm really confused and concerned, and i just really, really need help with this. Please help