Inaccessible Boot Device Error (W2K)

I run a dual boot system win98 and W2k pro, on separate physical partitions, Win98 on C: W2K on D:. They have work fine until I insalled W2K SP3, there were no problems durring installation, but after rebooting I got an “Inaccessible Boot Device Error”. I put it down to a bad SP and reloaded W2K again and tried SP3 from another disk but got same results. Can’t keep rebuilding.