安装AMP时我做错了什么?

So I am following TheNewBostons video guide:

https://www.youtube.com/watch?v=vQCIZOv1su0&list=PL6gx4Cwl9DGDdCg0Jli_WTZd5JIliDY62&index=3

(On how to manually install Apache, php and MySQL)

Getting to the 3rd video where I am about to make the "Tuna baby!" php file to test it out I get the error "404 Not Found". I don't have Notepad++ so I am just using Notepad and naming it .php at the end. If I only write localhost is says "It works!", so Apache is working.

Not Found
The requested URL /tuna.php was not found on this server.

The weird thing is that I had no problems while doing this on my main computer but now I am doing it on my laptop and seem to have the problem every time I try doing it. Had to uninstall everything with "Revo Uninstaller" to remove all the traces and so on so this should be a clean install.

Any idea why it is not working?

Installed Notepad++, saved the file properly as a php file and it worked.