ad popups appearing; mediaplex, pc-on-internet etc

I've just recently started getting pop up windows with no tool bar. I get asked to give permission for either pc-on-internet.com; fe.pc-on-internet.com or em.pc-on-internet.com. When I deny the cookie the window opens anyway. It's usually something mimicking windows security centre saying I've been infected with spyware and I should download spyware protection fom a link in the window. Needless to say I haven't. I also get other adverts like 'yesloansuk' or 'Alton Towers tickets' I've tried putting the various url's into my cookie handling but it doesn't do any good. I've deleted the various keys from the registry - no luck! I've scanned my systemwith Microsofts various tools but they came up with nothing. Can someone help?
By the way. I tracked down the pc-on-inernet.com website and it is something called '000 favorit' a Russian company - anyone know what the heck is going on? I previously noticed mediaplex or adfarm mediaplex urls in the ads. I'm going nuts, anyone know how to get rid of this

 

Try two scanners.

SuperAntispyware free
Malwarebytes Antimalware free