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critical HP

Error Code Red LED flashes four times, once every second

Power failure (power supply is overloaded). OR The incorrect external power supply adapter is being used on the unit.

? What Causes This

Overloaded power supply or wrong adapter

✓ How to Fix It

  1. Check and remove all attached devices while powering system to determine causing device, if system enters POST replace one at a time, continue until failure occurs.
  2. Replace power supply.
  3. In case of no effect, replace the system board.

Source: page 38 of the official manual

From the manual

Manual page 38 — HP error Red LED flashes four times, once every second

This error code appears in:

HP T630 Thin Client