The ornamental design for an all-in-one computer, as shown and described.
FIG. 1 is a front elevation view of an all-in-one computer showing my new design;
FIG. 2 is a rear elevation view thereof;
FIG. 3 is a left side elevation view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a front perspective view thereof.
The broken lines depict environment and form no part of the claimed design. In addition, the unshaded surfaces that directly adjoin the claimed solid line edges form no part of the claimed design.