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critical HP
Error Code No LED activity at all upon power on
System does not power on and LEDs are not active.
? What Causes This
General system unresponsiveness or hardware failure.
✓ How to Fix It
Perform comprehensive hardware check, replacing components as needed. Seek professional service if unresolved.
Source: page 2 of the official manual
From the manual
This error code appears in:
HP Prodesk 600 G1 Small Form Factor PC