FIG. 1 is a perspective view of a cover for the back of a personal computer tower showing my new design, wherein a personal computer tower and cords thereof are shown in broken lines for illustrative purposes only and form no part of the claimed design;

FIG. 2 is a right side elevational view thereof;

FIG. 3 is a left side elevational view thereof;

FIG. 4 is a front elevational view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a rear elevational view thereof.

The dashed lines on the cover itself represent stitching and form part of the claimed design.