The old way of resetting the 8051 was to use a 8.3k resistor from the reset pin to ground and a 1uf capacitor from Vcc to the reset pin.So that way the reset pin is high for a short while when the power is first applied,then goes low as the capacitor charges.Its not super reliable and the more modern method is to use a power supply monitor and or combined watchdog/brownout detector which holds the processor in reset when the voltage falls below a certain level.If you dont connect the reset pin at all it will just float high,as it has a weak pull up,and it will be stuck in reset which is why its not running.