To replace the hard drive I did the following, 1-Disconnect the battery connector 2-Afterwards replace the hard drive. When I switched on the MBP it did not turn on, so restart it I did the following, 1-Put back the old hard drive. 2-Switch on the MBP but it did not work. For SMC reset I followed the apple advice but of no use,the MBP did not turn on.One more thing when the charger is connected the light fade off after some time. Some body may rescue me from this situation. Take care.