Sometimes, programs are setup within the program itself to load when Windows starts. To find these programs, look in the tool tray on the right of the taskbar. The icons you see are some of the programs currently running on the computer.
To prevent a program from starting when Windows boots up, open the program and look for an Options Menu. This menu is usually under the Tools menu at the top of the program window (also look under the Preferences menu). When you find the Options menu, look for a checkbox that says “Run program when Windows Starts” – or something to that effect. Uncheck that box and close the program. The program should now not run when Windows starts up again.
For example, I have a program called “Samsung PC Studio 3” that synchronizes my phone with MS Outlook. As you see in the picture, the Options menu has a setting to run this program when Windows starts. By unselecting this checkbox, I avoid launching this program until I actually want to use it.