It looks like it will be in the configuration settings in the WiFi section for that particular computer. Depending on the type of WiFi hardware fitted, you may be able to dive into theses settings and see whether is has a default WiFi network it expects to connect to, or whether it does a search every time it boots. It may have accumulated a stack of WiFi networks in a former lifetime, and expects to search through these for a previously preferred service. If you can, clear any such list, and once you have connected to the one you want, see if there is an options to "connect to this service automatically" or similar. It's hard to be more specific than this because these parameters can and will vary according to hardware and OS combinations.