Thanks to chkdsk command...
I had accidentally unplugged the power of my PC at office while it's
running.
At first, I thanked GOD that I wasn't in a middle of a long programming
task. I plugged the power again and started the PC, unfortunately the
windows couldn't start at all, even on safe mode. After a while I
decided to use the Windows XP CD, but I don't know why the setup
couldn't read the file system on C drive, and suggested to format this
drive even when I tried to install a new Windows version on D drive. Of
course I will never format a drive while I don't have a recent backup
of the data.
As a final solution I selected the Repair option using the Console during the
Windows XP setup, and a DOS cmd was lunched, I couldn't access c drive
and I get a file corrupted message, but when I tried CHKDSK command to
check C for errors I was surprised that it could be able to start and
check the disk for errors.
When restarting then everything was alright. Thanks chkdsk you save my PC.