msconfig has a section of all the programs that open on startup. so if you talking about a program that opens on startup then just take it off of the list.
if your talking one that opens randomly and not at startup theres either A: a program opening the program, or B: a trigger from a website, or a connection your your computer, or something like that.
so disable all programs you dont recognize at startup, and if that doesnt work, disconnect your computer from the internet and see if it opens up then, if either of those answer it, then you know what the cause is and can find an answer.
or if you just dont want someone opening a program on your computer, install it somewhere in your documents, and allow access to your documents to only you, and dont install shortcuts