critical HP

Error Code Red LED 6 blinks every second followed by a 2 second pause

Indicates a pre-video graphics failure before the POST phase.

? What Causes This

Faulty video hardware or incompatibilities with the installed graphics drivers. Memory related issues may also cause this issue before video card initialization.

✓ How to Fix It

Re-seat or replace any faulty components, especially memory and graphics cards.
Perform a system test to rule out software causes before replacing hardware parts that could be at fault.

Source: page 4 of the official manual

From the manual

Manual page 4 — HP error Red LED 6 blinks every second followed by a 2 second pause

This error code appears in:

HP Elitedesk 800 G1 Small Form Factor PC