For some reason your computer is not starting from the harddisk, this could
have various reasons.
1. Your harddisk is defective
2. Your harddisk is not being detected by the BIOS
3. Your BIOS is ill-configured and does not have the harddisk in the boot
sequence
4. Your harddisk is empty (ie doesn't contain any bootable partitions)
5. Your XP partition is not marked as active...
What to do, firstly check whether the BIOS detects the disk at boot-up, it
should be in a litlle listing showing you all IDE devices attached. If it is
detected and you feel confident going into the BIOS, do so and check that
the boot sequence includes the harddisk. If that's all ok then you either
haven't installed XP yet or the harddisk structure has become corrupted. In
the case that you know for sure that there is an XP installation on the
disk, then boot from the Windows XP cd and enter the recovery console, run
the commands fixboot and fixmbr and see if XP will boot now.
It might help if you can give any more details on how this happened exactly,
what you did or didn't do, etc.
Regards,
Wichetael