Quite common, maybe the pc didn’t shut down properly and some data got corrupted.
But usually quite simple to fix if you have a Windows XP disc.
First you need to boot the pc from the windows cd. You may need to change a setting in the Bios to make the DVD /CD drive the first boot device.
When the pc starts from the cd you will get a option to start the recovery console.
Do this and then you end up with a DOS type command prompt.
You will need to type in the check disc command (chkdsk /f ) and it will scan your volume and should fix any errors.
When it is finished , remove the windows cd an restart as normal.