Dell Precision T7400 (Late 2007) - Manual (Page 158)

158 Adding and Replacing Parts
11 Pivot the socket release lever back toward the socket and snap it into place
to secure the processor.
12 Clean the thermal grease from the bottom of the heat sink.
13 Apply the new thermal grease to the top of the processor.
NOTICE: If you are not installing a processor upgrade kit from Dell, reuse the
original heat-sink assembly when you replace the processor.
If you installed a processor replacement kit from Dell, return the original
heat-sink assembly and processor to Dell in the same package in which
your replacement kit was sent.
14 Install the heat-sink assembly:
a Place the heat-sink assembly back onto the heat-sink assembly
bracket.
b Rotate the heat-sink assembly down towards the computer base and
tighten the four captive screws.
NOTICE: Ensure that the heat-sink assembly is correctly seated and secure.