!!
critical HP
Error Code Red LED blinks 4 times every second followed by a 2 seconds pause
Power failure (power supply overload).
? What Causes This
Overloaded power supply or inadequate electrical connection/output.
✓ How to Fix It
1. Unplug and check connections to the power outlet, ensure proper wattage supplied.
Source: page 2 of the official manual
From the manual
This error code appears in:
HP Compaq Elite 8300 Small Form Factor PC