What would cause a 1995 Toyota Camry to overheat and the heat not work?

I would say no thermostat as to the heater not working,unless someone has bypassed the heater. Funny thing is I just bought a 1995 Camry LE . Starts and runs great, drive for10 miles around town or 40 country .Then SOMEHOW its lost water and got hot.I replaced water pump and radiator,still problem persists.I can tell a previous owner hot rodded the car.I'm about to pull the head off,I'd rather not if someone knows of what else it could be, PLEASE help I am at Mountainbudman@Yahoo.com