Start up problem help needed

Dear All,

for last few weeks my 4 year old macbook 10 showing black screen at start up while I can hear fan sound and sleep light on. It would only boot after some 20 minutes after several attempts. I have done smc, pram, restarted with safe boot but no help. also hard ware test showing no problem with hardware. I have also done repair disk. after start up system behaves normally but when I shut down and again press power button to start the same problem as mentioned above - black screen, fan sound, light on but no boot sound.
is this software problem? will taking backup and reinstalling software help?? Please help.

Thanks & Regards,

Back up everything now, yes! I'm no IT pro, but I'd bet that your hard drive is dying. I don't think reinstalling all your software is going to make a difference.