First place to look is in the options or preferences of the programs that
are starting. Turn off "start when Windows starts" or similar language there.
About 3/4 way down the page he gives a list of links to start-up
manager programs.
Or you can use Windows msconfig to see what programs are starting up
at startup. Click "Start", select "Run" and type in msconfig and click
"OK"
After you see what is actually starting up at boot, you can see what
they do by downloading this list of just about everything that might
be starting up:-