I need a good imaging backup program. Any suggestions?

So, I'm not a dummy when it comes to IT, it's just I've recently changed over to PC and just don't know the programs for Windows.

So, I would like a program that will make a complete image of the computer HDD and back-it up to an external drive. So, if something happens to my internal HDD, I don't need to re-install Windows or anything annoying or silly like that, and can just go ahead from where my last image back-up was.