When you boot up your Mac, I assume the icon for your internal drive shows up on the desktop. With that being the case, double click on that icon. You should see the following folders, at a minimum:
Applications
Documents
Library
System
Users
Click on the one for Library, and you'll then see a number of folders. Scroll down to the one that says Startupitems, and double click on it. It should show you any Startup programs.
If the one you want is not there, double click on the one for System. Next, you'll see a screen which has (at a minimum) another Library folder. Double click on that, and follow the same procedure as above.
If you still don't see it, then I wonder if you have a Permissions Issue. Not sure about that, and maybe someone else can help you further.