When on a Windows computer, I almost always use Notepad++ for all the text editing and casual coding needs. While an excellent text editor Notepad++ is missing some of the key functions often desired in source code editors. Instead you can use another open-source text editor called CudaText which offers syntax highlighted code editing for all the popular programming languages. It shows a code tree on the left side which makes it very easy to navigate through the source code file from one node to another.
Even though CudaText is focused on programming languages, it can also be used for casual text editing. And since it is offered in the portable format, you can keep it somewhere on your hard drive for anytime text editing needs.
You can download CudaText from http://uvviewsoft.com/cudatext/.