Hard disk not spiinning due to SMPS fault

Today one of my costumers PC  I found the following problem A message on  the screen saying that there is no bootable disk.
To troubleshoot I did the fallowing procedure
1) open the case
2)check the hard disk. i cannot sense any vibration of hard disk spinning. and hear small moaning from the disk.
3) check voltages in power cable for hard disk , found the 5 V supply is less than normal
4) evidently there is  some problem in 5v regulated supply of  SMPS  power supply.
5) Replace the SMPS  box with new one solved the problem
6) Hard is now spinning.and computer booting without any complaints