Steam is always updating itself in the background and often downloads shit I definitely don't need or want. Unfortunately, there is no way to stop it short of uninstalling but if I do that I can no longer play the games I purchased through them. On the other hand, millions of people use Steam so I'm thinking some other Winstep user/s might have had the same issue if it had been the cause.

Why o Why do you have steam running at startup? disable it at startup and run it manually when you want to play, unless you really, really, really want it to run automatically for convenience of automatic updates or messaging.