[FatBoy]

Do you have another PC available?
If so, you could try installing the disk drive from the faulty PC into the other PC as a secondary drive. You may need to change the jumper settings on the drive to identify is as a "Secondary "drive. Simply connect it using the same ribbon cable (there should be a spare connector on the cable) as that used for the existing drive and use one of the spare power connectors.
You should then be able to boot up the PC and the "new" drive will be available as an additional hard drive i.e. D: If this works, copy your daughter's files onto the C: of the computer so that they are protected and safe.
If it doesn't work, the fault maybe with the hard drive itself. There are a number of utilities available that may allow you to recover data from the drive.
Alternatively, you could try booting the faulty PC with your Windows CD inserted. It will then give you the option to install Windows, which will give you the option to format the drive. DON'T do this until you have copied any required files to a safe location. It should also give you the option to Repair a Windows installation. Give this a go and see if it works.
Report back.

I hope that helps.
Paul