I had that problem because my modem connection could not ahndle the speed of 90V and I had to reduce it to 34V (it should be under Network settings.

Green light and then within a minute a disconnection-knocked me right off the internet every time unless it was very early in the morning and not very busy (6AM) Same problem with AOL and Earthlink.
I don't know if you are slow phone dial up or DSL, or cable , howeverI am slow phone dialup and it can be very frustrating.