Why isnt my motor cranking over?

The main fuse on the positive battery cable was blown from connecting the battery cables backwards while getting a jump. I Replace it with a new one from the dealer and the motor still will not turn over. And I cant take the key out of the ignition. Checked the fuses. found that the ignition and the starter fuses are good but have no power to either side of the fuses, it seems like i have no power to those slots in the fuse box. all other fuses are good even under the hood. what can i check to see why i am not getting power to those slots in the fuse box. that control the starter and the ignition. Thanks.