Hal.dll file missing and cannot boot to any CD (XP)

For no apparent reason this error has occurred on my wife's PC and after Googling everywhere I have found that the most common solution is to simply insert the Installation CD into the PC and then respond to the "boot from any CD" prompt and after that I think I could fix it all OK...........

But I can't get the "boot from any PC prompt" up i.e appears the system is not finding the Windows disc and then reverts to the error message!

I have tried the F5, F8, pressing DEL or TAB during the reboot but no joy!

Help!!:(:o