info HP

Status LED 3 blinks at 1Hz followed by a pause of 2 seconds (Green LED)

System in Stand By mode.

? What Causes This

Operating system or user settings controlled the standby behavior.

What This Means

Press computer's power button to resume operation from stand-by state.

Source: page 27 of the official manual

From the manual

Manual page 27 — HP error LED 3 blinks at 1Hz followed by a pause of 2 seconds (Green LED)

This error code appears in:

HP Compaq Pro 6300 SF Desktop