Dell OptiPlex 755 - Manual (Page 225)

2. Reconnect the cable to the system board.
3. Replace the computer cover (see Replacing the Computer Cover ).
4. If you are using a computer stand, attach it to the computer.
Resetting the Chassis Intrusion Detector
1. Turn on (or restart) your computer.
2. When the blue DELL™ logo appears, press <F2> immediately.
If you wait too long and the operating system logo appears, continue to wait until you see the Microsoft® Windows® desktop. Then shut down your
computer and try again.
3. Select the Chassis Intrusion option and then press the left- or right-arrow key to select Reset. Change the setting to On, On-Silent, or Disabled.
4. Save your BIOS settings and exit system setup.
System Board Components
Cable Cover (Optional)
NOTE: The default setting is On-Silent.
1 fan connector (FAN_FRONT) 8 password jumper (PSWD)
2 internal speaker connector (INT_SPKR) 9 hard drive fan connector (FAN_HDD)
3 system board speaker (BEEP) 10 clear CMOS jumper (RTCRST)
4 channel B memory connector (DIMM_2) 11 hard drive power connector (SATA_PWR)
5 channel A memory connector (DIMM_1) 12 fan connector (FAN_REAR)
6 SATA data cable connector (SATA0) 13 intrusion switch connector (INTRUDER)
7 battery (BATT) 14 processor (CPU)