Yes there is an alternative to Re-Formating. FIXBOOT AND FIXMBR! What you will need is the O/S disc. (A Win XP disc)
Go ahead and boot from it and when prompted press "R" do do a repair with the recovery console, next you may be asked which partition, select your C:\ drive (In most cases it doesn`t give you options, just press enter if asked) then when prompted type fixboot and press enter, then type fixmbr and press enter Viola! you just repaired the boot sector on your HDD and also rewrote the master boot record for XP, it should boot then!