Dell Vostro 420 Service Manual page 49

4 Holding the cover at a slight angle, slide it toward the front of the
computer until the metal clips inside the cover grip and attach securely to
the chassis frame beside the front bezel.
5 Ensure that the cover is seated and aligned correctly.
6 Replace and tighten the two thumbscrews that secure the computer cover.
7 Follow the procedure in "After Working on Your Computer" on page 45.
Computer Cover
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