We claim the ornamental design for a desktop computer, as shown and described.
FIG. 1 is a perspective view of a desktop computer showing our new design wherein the lines shown on the front panel of the computer are understood to represent a pattern;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left-side elevation view thereof;
FIG. 5 is a right-side elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines depict portions of the desktop computer that form no part of the claimed design.