Are you using Avast or any other virus online security if so has it got an extension active in your browser saying no tracking?
This would stop the ads appearing.
As I said content (I suppose I should have been clearer and say this means the content of the page you are browsing and the ads are on) and of course cookies are landed on your computer from adverts too and these can be used to serve ads by Google (not all ads are Google ads and work in a normal...
As a Google adserver myself the bad news is, yes they do relate to the cookies on your PC, but if the cookies are cleared then they have nothing to go on so will go on content/page history. Equally if they have nothing relevant to your cookies (most recent first) then they will serve stuff...