Dear,Shahzad Aslam
please check the following

1)power 5volt (max+/- 20%)
2)check oscillator works
3)EA/VPP is connected to vcc+ (pin no31)
4)reset connection
5)connect the LED series with 1k resistor
cathode to 89c51 port & resistor end to vcc

good luck

P.Ashok Kumar