For this read this article in which everything is explained about system hard disk Things You Must Know About Your Computer Hard Drive.
IF this Blue Screen is comes on your computer monitor “the hard drive can't be accessible” it means your system now infected with some problem then from here your hard work starts because this is very irritated situation and everybody wants to remove this error as soon as possible and get out from this unwanted situation.
What are the reasons for inaccessible Hard Drive ?
Hard drive is a mechanical device and any error can anytime in the system if something is not according to operating system. We have to diagnose our hard drive to check and make free from any virus, trojan or any malware suspected program. You installed any new software firstly removed that program. In this situation generally you do reboot the system. May be from hard drive corruption .
Run CHKDSK/F this command check your all hard drive corruption and rectify after that you can Restart the system. Your computer hard drive can get into the normal situation.
Normally most of people format the hard drive when every step or method is not proved. This result of all data lost which is stored in hard drive. And this point of time you need some trusted hard drive data recovery software which is able to recover your all lost data from formatted drive. Stellar Phoenix Windows Data Recovery is the trusted name in the hard drive recovery from the last 17 years in world. This hard drive recovery software supports windows7, XP, professional, 2000 , & moreover more than 185 file formats.
Resource - http://www.programmersheaven.com/user/Kmadhav/blog/6016-How-to-Recover-Lost-Data-from-Inaccessible-Hard-Drive/