HP ProOne 400 G1 Maintenance & Service Manual page 140

Computer will not start.
Cause
Wrong memory modules were used in the upgrade or
memory modules were installed in the wrong location.
Power LED flashes Red five times, once every second, followed by a two second pause, and the
computer beeps five times. (Beeps stop after fifth iteration but LEDs continue flashing.)
Cause
Memory is installed incorrectly or is bad.
130 Chapter 9 Troubleshooting Without Diagnostics
Solution
1. Review the documentation that came with the system to
determine if you are using the correct memory modules
and to verify the proper installation.
NOTE:
DIMM1 or XMM1 must always be installed. On
all computers except the USDT, DIMM1 must be installed
before DIMM2, and DIMM3 must be installed before
DIMM4.
2.
Observe the beeps and LED lights on the front of the
computer. Beeps and flashing LEDs are codes for specific
problems.
3. If you still cannot resolve the issue, contact Customer
Support.
Solution
CAUTION:
To avoid damage to the DIMMs or the system
board, you must unplug the computer power cord before
attempting to reseat, install, or remove a DIMM module.
1. Reseat DIMMs. Power on the system.
2.
Replace DIMMs one at a time to isolate the faulty
module.
NOTE:
DIMM1 or XMM1 must always be installed. On
all computers except the USDT, DIMM1 must be installed
before DIMM2, and DIMM3 must be installed before
DIMM4
3.
Replace third-party memory with HP memory.
4. Replace the system board.