Hi:
See chapter 7, page 114 of the service manual for the beep code interpretation.
Maintenance and Service Guide HP EliteDesk 800 G2 SFF Business PC
3.4 The system board displays a power failure (crowbar).*
* Indicates hardware triggered event.
Troubleshooting steps...
Hardware | 3.4 | The Main-Board displays a power failure (crowbar).* Indicates potential power system failure. | 1 Reduce to minimum config (CPU, Main-Board, PSU, Single memory DIMM) and isolate failed component. 2 Reduce further if issue persists. 3 Test known good PSU. 4 Replace affected component. 5 If unable to confirm source, replace CPU, Main-Board, PSU. |