Actually, there are various reasons that cause data loss; software, hardware, factitious, natural, intended, unintended, all may cause data loss or damage on storage devices.

Software is the one of the two main reasons for data loss.

When it comes to software, you hear these words, Virus, format, mis-partition, mis-clone, mis-operation, network deletion, power-cut during operation all may be the software reasons. The symptoms are usually mis-operation, read error, can not find or open file, report no partition, not formatted, password lost and troubled characters.

Computer Viruses: some malicious virus programs will destroy data, overwrite, or erase the data contents.

Mis-format: fast or completely format partition, thus changing the file system form (NTFS, FAT32) of partition.

Mis-Clone: when backing up the hard disk, mis-clone or overlay the original data on hard disk.

For these, we can use software tools to recover it. So called soft recovery means data can be recovered by software, not referring to hardware fixing operation for its fault is not because of hardware failure.

The following are prompts that system can not start up normally:

Invalid Partition Table: Invalid partition table information.

Missing Operating System: “55AA” mark in DOS boot sector lost or DBR corrupted.
Disk Boot Failure: System file read failure. Bad or missing command interpreter: Can not find command.com file or ‘COMMAND.COM’ file corrupted.

Invalid system disk: DOS boot record corrupted.

Type the name of the command, Interpreter: DOS partition mark in partition table error or ‘COMMAND.COM’ file lost, corrupted. Error Loading Operating System: Main boot startup program read boot sector unsuccessfully. Not found any active partition in HDD: Active partition mark in partition table changed as inactive partition mark.