On many vehicles the computer 's system voltage comes from a relay or fuse. The system voltage should never be less than 9 volts while the starter is cranking the engine nor greater than 15 volts while the engine is running. If the voltage is not within the 9 - 15 - volt range, some computer will shut themselves down.
Check the relay or fuse.
Also inside the computer is a voltage regulator which reduces the system voltage to a constant reference voltage of aproximately 5 volts. No matter what the system voltage, the reference voltage will allways stay constant. The voltage regulator's second purpose is to shutt off curent flow if there is a short circuit. This may have caused high curent flow in the circuit and the computer will not work untill the sensor is replace. Follow the manufacture's recommende diagnostic procedure to locate the bad sensor and do not make quick decision to replace the computer.