Stop 0x23: FAT_FILE_SYSTEM
Corruption in the file system or bad blocks (sectors) on the disk can induce this error. Corrupted SCSI and IDE drivers can also adversely affect the system's ability to read and write to the disk, thus causing the error.
Another possible cause is depletion of nonpaged pool memory.
If the nonpaged pool memory is completely depleted, this error can stop the system. However, during the indexing process, if the amount of available nonpaged pool memory is very low, another kernel-mode driver requiring nonpaged pool memory can also trigger this error.
DO you have a Boot Floppy or XP CD you can start from?
You need to get into Recovery console and run chkdsk /f