The usual problem is that you aren't opening the file you think you are. Name your edited file something different, like my_Not.hdl, and load that file and see if you are able to see the changes. You won't be able to run the test script because it is looking for the original name, but this will let you see if you are looking in the wrong place.
When you save the file in Notepad, are you explicitly including the ".hdl" extension to the file name? Unless you do this, Notepad applies the extension ".txt" by default. This snap from Windows File Explorer shows the same file with the ."hdl" and ".txt" extensions, respectively. I still sometimes forget to add a necessary extension when I create new files in Notepad.
I have the exact same problem!
I am running the Hardware Simulator with OpenJava on Windows 10.
When I load for exmple the Not.hdl file from the \nand2tetris\projects\01 -folder it loads fine but if I open the Not.hdl with notepad and starts to write a just a single character after the line: "//Put your code here:"
and saves it with just the .hdl extension Then trying to load it in the Hardware Simulator it just says "Loading chip..." in the status line and the file Not.hdl never loads.
If I the open the Not.hdl with notepad again and removes whatever I have written after the line: "//Put your code here:" - restoring the file to its original contents and saves it again. Then the Hardware Simulator loads the file fine but without my code. Then it is a bit hard to finish any of the projects.
Please can anybody help!!!