Dell Precision T5400 (Late 2007) - Manual (Page 31)

About Your Computer 31
1 Follow the procedures in "Before You Begin" on page 151.
2 Remove the computer cover (see "Removing the Computer Cover" on
page 153).
3 If converting from a tower configuration to a desktop configuration, find
the spare card retainer beside the card fan, pull its retention tab out from
the surrounding metal and pull it up, away from the chassis.
Desktop Orientation
Tower Orientation