Dell OptiPlex 5055 Tower Owner's Manual page 43

b power switch [2]
c speaker [3]
d PSU [4]
e power distribution for optical drive and hard drive [5]
f system fan [6]
g intrusion switch [7]
7 To remove the system board:
a Remove the screws (6+/-1) that secure the system board to the computer
Disassembly and reassembly 43