SWC0700: iDRAC is not ready. The configuration values cannot be accessed.

Hello, Please try below troubleshooting steps. 

to power drain

Shut down server.

Remove power cable (all power cables if there are redundant power supplies)

Hold the power button in for 15 seconds.

Reconnect the power cables.

Wait 2 mins(this is to give the iDRAC time to initialize)

Restart the server.

Resetting iDRAC https://dell.to/3K4PvWi

Checking NVRAM clear https://dell.to/3FTFUBd

If you have iDRAC port card please reseat and check again https://dell.to/3Lqc5Jm

If you don't have iDRAC port card then to take the server to minimum post configuration

The minimum components to allow the PowerEdge R420 to complete POST are:

• System Board
• CPU1 with heat sink (minimum for troubleshooting)
• Single DIMM configuration with DIMM in socket A1
• Control Panel with cable (to power system on)
• Expansion Riser
• PSU (and for redundant PSU also the PDB/PIB)

If the above troubleshooting steps don't help I would suspect a hardware error. It could be iDRAC port card or motherboard. If you need iDRAC port card part number is 2827M 

Hope that helps!