One possibility could be a broken OVP relay, or a blown fuse in the OVP relay. It is clustered with a couple of other relays behind a black plastic panel behind the battery. It is the relay with the red top and a fuse underneath a clear plastic cap. Check the fuse. A search for OVP or "overvoltage protection" relay should bring up some more information.

There could be also a number of other reasons for this, and you should probably find a good shop if this isn't the problem.