Your post is very generalized, so it's hard to provide useful help with what's stated. Given this, if you comb through the boot up services and identify any 3rd party programs that might use the Internet, jot them down. Once you've done this, modify their entries in services.msc to "auto start delay". That may help you.
If you really don't know where to begin, you can try disabling all start up services, then enable them a few at a time until you start seeing the lag. This should help give you an idea which one(s) is(are) the culprit.