!
error HP

Error Code LED flashes Red three times then White four times.

Power failure (power supply overload).

? What Causes This

Overloaded PSU due connected devices, unbalanced power source, or faulty components.

How to Fix It

  1. Ensure correct voltage setting based on geographic location using selector switch if equipped.
  2. Confirm system board connector seating for power cable.

Source: page 79 of the official manual

From the manual

Manual page 79 — HP error LED flashes Red three times then White four times.

This error code appears in:

HP Prodesk 400 G3 Desktop Mini PC