Check incoming power. Confirm that the power cord(s) are securely connected at both ends and the incoming power source is known to be operational an within the required specifications. Reference specific system using the online Oracle System Handbook. Select Hardware Specifications under Information Areas for exact power requirements.

For systems with a physical keyswitch, make sure the system key in the keyswitch is set to the Normal or Diagnostics position when pressing the On/Standby button. Turn the keyswitch to the locked position to prevent the system from being accidentally tuned off. Remove the system key and store it in a secure place. A limited number of systems have an interlock switch which could prevent a system from powering on. To see if the system in question is affected reference: <Document: 1011578.1>

Verify there have been no changes to hardware configuration such as an additional system board or power supply taken from a spare system. System boards with USIII or USIV are not interchangeable and may interfere with a system powering  on. Also note that power supplies used in systems with USIII CPU's are not compatible with USIV CPU's.          

If the system still does not power on the issue may be with the power supply(s) or the power distribution board. Reference: <Document: 1010045.1>