No power

Hi I have a 1996 oldsmobile bravada, 4.3Li with 114.000 miles. The problem I am having with my car is that I am not getting any power to the entire car! I recently replaced the head gaskets. But since after I reassembled the motor I have not been getting any power, but I think this happened before the gasket replacement. The battery has charge (tested @ 12.73 volts). I checked the fuse box inside of the car and it is dead no power at all? The instrament cluster does not work, inside lights, horn, break-lights, wipers, door chime, nothing? Things that does not even have anything to do with the engine, I turn the key and nothing. Please help. I would like to know where the primary fuse is located, and or the power distribution center? I need help! Thanks