There are number of reasons why data could be lost:

• OS corruption
• OS re-installation
• Hard drive failure
• Improper computer shutdown
• Disk partitioning
• Accidental formatting
• Accidental deleting
• Virus activity
• And much much more...

• First of all - DO NOT PANIC! Panicked user often is more dangerous than any virus or threat. So keep calm and follow these instructions:
• Don't run any programs
• Switch off all programs
• Shutdown computer
• Do not switch on computer and do not use it in any case or you may loose data irrevocable.
• Contact IT specialists, for example - us ;)