Juicy one this...

Put your XP cd into your cd rom mounted on the same bus as the hard drive and boot from it...Get to the point where you are asked to take the option "R" to enter the recovery consol.

Press '1' for your main installation and then enter the administrators password or press enter if you have no password...

See if the recovery consol enters the c:\windows\ directory. If it does goto root directory and type in "Chkdsk<Space>/p"
let the program run and then when its finished exit the recovery consol and boot normally.

if you have no success go into the bios and check the dive is listed under the cmos settings. If not set it to Auto if you can. If you cannot do this use the user parameters and enter the parameters from the drive lable into the BIOS, you can alternatively set default settings and exit the utility after saving the values to the cmos.

Try to boot the pc now...

If all is not right, check the hard drive IDE cables are in tightly on the motherboard and the drive itself and the jumper settings are correct on both IDE channels.

Jase