3rd master hard disk s m a r t at startup

Your system is telling you that the hard drive is getting ready to fail. And you need to backup the data on it and replace the drive.

http://www.harddriverecovery.org/smart_detection.html

Ignore the warning at your peril.

Pretty much sums it up --- the HDD is reporting that it is about to die so you need to backup your data and replace it !

thankxxxxx friends...      

how to prevent these type of failures......

Really isn't much that you can do --- HDD's are made up of materials that eventually deteriorate due to usage and eventually they get to a point that the magnetic disks can no longer keep the data intact perfectly and start to have errors in various spots (though too much Heat inside the system, Dust build up on the HDD, inconsistent Power due to either the local electric company or your PSU, etc. etc. can cause failure to occur more rapidly) and while the newer drives have gotten better at redirecting the data to a good portion of the disk eventually it gets bad enough that the drive will fail to perform within the specifications set by the manufacturer and it will begin to fail the SMART checks and give you the error you are getting. How old is the HDD ? If it is still under warranty you can get it replaced by the manufacturer but will still need to get any info you need off of it before sending it in for replacement (If it is not then it has probably just reached it's useable life span and is time to replace it anyway.

At least it has given you some warning and time to get any vital info backed up instead of just failing (which happens at times as well)