Startup

A lot of programs start automatically.
System Configuration gives you an overview.

You can access it using Control Panel > All Control Panel Items > Administrative Tools

You can use this to disable programs and do a reboot.

An easy way to prevent programs from starting is using the Registry.

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run and

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

contain the programs that start when you power on the system.

You can add this locations to Favorites.

A good practice is to export this part of the Registry before you make any changes.
A simple way to prevent programs to start is to choose Modify

Simply add a ; in front of the value.

No need to clear it or to delete the entire key.

The most effective way to prevent a program from starting is to uninstall it.