Dell OptiPlex 755 User Manual page 158

1 securing tabs (2)
2 hard drive
8. Disconnect the power and data cable from the drive.
9. Disconnect the hard drive fan cable from the system board.
1 power cable
2 SATA data cable
Installing a Hard Drive
1. Check the documentation for the drive to verify that it is configured for your computer.
NOTICE: To avoid damage to the drive, do not set it on a hard surface. Instead, set the drive on a surface, such as a foam pad, that will sufficiently
cushion it.
2. Unpack the replacement hard drive, and prepare it for installation.
3. If your replacement hard drive does not have the plastic drive bracket attached, remove the bracket from the existing drive by unsnapping it from the
drive.