!!
critical HP
Error Code Power LED blinks red, 6 blinks with a pause
Pre-video graphics error detected during boot.
? What Causes This
Graphics adapter failure or driver issue.
✓ How to Fix It
Reinstall/upgrade graphics card drivers. If unresolved, replace the motherboard/GPU.
Source: page 2 of the official manual
From the manual
This error code appears in:
HP Prodesk 600 G1 Small Form Factor PC