DO you have Windows 98? if so Make sure there is no floppy disk in the floppy drive. If you have one.
Boot with a 98SE bootdisk and at the A:\> prompt, type in;
sys c:
If this doesn't work, boot with the bootdisk again and at the A:\> prompt type in;
fdisk /mbr
If you have Win XP boot from the cd and enter the Recovery Console and type
fixmbr
Post back with your results.