Hi Coollifeinindia

when you say 5 in 10 times, means something else to me. other than your Hard drive.

I would say it's your Power Supply failing, Not your Hard Drive.
Because, if it was your Hard Drive, then it would be all the time, and you would have had to Reload the Windows several times.

I know it can be hard to diagnose this problem, so, I would recommend the following to properly diagnose.

1) Re-Install Windows, BUT this time, Delete all Partitions, and installed into the remaining unpartitioned space available. (IF YOU have a RecoverY CD do not do this)
This will erase the Boot sector and rewrite the MBR fixing any Boot secort errors.

2) Update the Firmware of your Motherboard.
This will ensure power Management to ob-board IDE controlers are managed correctly.
by the way did you install a NEW Hard Drive?

3) Install a NEW Power Supply over 430 watts.

Now tell me what happens.
If you can, please list ALL COMPONENTS in your PC, and how Many Watt Power Supply you have at the moment?

Look forward to your reply.
Take Care
DN