Kamla, since there was no storm damage(and the sub probably wasn't even moved)a specific answer doesn't immediately spring to mind. The fuse blows because too much current is going through it, but what caused this is some type of internal short. A connecting wire inside may be loose, or the voice coil of the driver may be damaged(check it by gently pushing the cone in to see if it moves smoothly without a grating sound). Or, the supply section of the sub amp may itself have developed a defect, which Axiom should be called about.

Enjoy the music, not the equipment.