The error message "UNMOUNTABLE_BOOT_VOLUME" does not necessarily mean that the hard disk is defective,it may be simply a problem on the sequence of the disc.
To fix this problem, insert the Windows XP CD and boot your computer (make sure your computer boots from the CD of Windows XP).
When it arrives on the interface giving a choice between "installed entry" and "repair", press "R".
If the Recovery Console asks you what version of Windows you want to check, try typing the number 1 and then confirm by clicking the "enter" then if it asks for a password, click on the "enter" without scoring password
Then when the console displays
C: / windows
type the following command (beware there is a space before the signs / R / P):
CHKDSK / R / P
Once the scan is complete, enter the following command:
Validate by clicking on entry and then type the letter O and confirm.
Then type the command "exit"
then eject the Windows CD and restart your computer.
UNMOUNTABLE_BOOT_VOLUME the error must be resolved