Console Is Booting directly to Bios
Console immediately displays the Bios screen after being powered on and does not continue to boot normally. This can be applied to any console.
Power cable running to the hard drive is not seated correctly or disconnected. (Most Likely)
SATA Data cable running to the hard drive is not seated correctly or disconnected.
To check if the Power Cable and SATA cable are seated correctly/connected, unscrew the back panel of the console and locate the hard drive.
Some consoles require you to lift the screens forward to access the hard drive.
Once located, check the connection of the two cables running to it. See the picture below: