Sounds like your overvoltage protection relay (fuse-capped relay in the firewall behind the battery) has bit the dust. Well, either that, or the fuse has blown. If you do a search here for "overvoltage relay" or "OVP" you'll find a lot of information on the relay. stevebfl has posted some good info on it.
The good news is that if it is the OVP relay, it's not that expensive, and a straightforward replacement. The bad news is that it's a bear to pull out of the socket.