NTFS filesystem can become corrupt/unusable because of various reasons. In such situation windows file manager might not detect this partition. One such situation I encountered was during formatting my laptop from Windows to Linux to Windows. The non-bootable partition of my laptop was rendered unusable.
Before going into the solution, one important property of NTFS. NTFS maintains an extra copy of the boot sector. This extra copy eventually helped me to recover my data.
One of the first tool to use is windows utility ‘chkdsk’. On running windows utility chkdsk, it pointed to the problem ‘NTFS boot sector unreadable’. Using ‘chkdsk \F’ didn’t fix the problem. After some googling I came across a rather very simple tool – TestDisk. Its an opensource software with GNU General Public License. TestDisk copied the spare boot sector record to the primary boot sector and after a restart my hard disk partition was detected successfully and my data intact. Using TestDisk is simple and well documented on the website.