Irritating search options popup

[rock1]

I'm using windows 7 32 bit. over past few days when i start my computer i get the following box.

I originally had google as my default search engine but now windows automatically sets yahoo as default on startup inspite of changing it to google numerous times. i've played with both the tickbox options in this box but i fail to change my setting and this box popups upon startup . what should i do ?