My experience (and i also work in IT, as a programmer):
It's about my mother's internet connection. I go to my birth town like once a month, after she payed for the subscription and got the ASDL modem I was there also bringing a wirless router trying to setup the connection. Unfortunately was weekend and they didn't activated the account yet. I configurated everything but coudn't test and instructed someone else to complete the process.
After the account was activated my mother reported that using wireless she can access internet only few seconds after starting the laptop, and the only way to stay connected was to plug in the modem directly to the laptop. When I visited second time i found out that only by connecting the modem with the usb cable to the laptop worked, network cable didn't work (coudn't access the http setup for the modem if it was connected with network cable)
I called support center and went trough the lan settings and coudn't find anything wrong. Unexpectedly a field technician was in the area and he payed us a visit in a few minutes (lucky us). He had with him another modem and a laptop. The new modem didn't worked on my mom leptop, both modems worked on his laptop. He sayed the the modem they gave us is ok, and is not his bussines to debug my computer, especialy that i wished to use a wireless router in the setup.
Funny part is that he blamed my network card (malfunctioning or drivers not properly installed he sayed) and was pointless to me to show him live that if I connect the laptop using network cable to the wireless router (which also has 4 lan ports) it worked...he didn't care about what he could see with his own eyes, just that is not his job to debug my computer nor he cared about the wireless routher cause is not from their company.
After he left I just decided to use a needle (for that hidden button) and reset the modem to factory settings. You can imagine that it worked from the first reconfiguration attempt.
So...never underestimate those equipaments