I'm sorry it's been difficult. Which version are you trying? Are you trying on shared hosting or your own VPS host or something similar? v7 uses Laravel, whose hosting requirements are a little different. A 404 to the installer likely means that the htaccess isn't setup correctly by your host, or your host is blocking htaccess from working properly.
If you can give more information, we can try to help you figure out what the issue is.