Dell Latitude C400 Replacement Instructions Manual page 11

Close the display, turn the computer over, and replace the two 6-mm
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screws at the back corners of the computer.
Turn the computer right-side up, open it all the way, and replace the
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center cover:
Carefully position the cover, and then press down first on the center
and then on the back ridge of the cover to snap those areas into place.
Then press the rest of the cover down, working outward toward the
ends.
To replace the battery, slide it into the battery bay until the latch
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release clicks.
Replacing the Display
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