PLC Allen Brandley

I have the this error on my screen Error 208, showing the inability of the CPU to communicate with the field Devices.How can i correct it.
If i have the backup of the cpu, can i re-load it
The PLC is SLC 504 with PV900, DH + comm.
Again somebody mistakely power-off the processor and the PV.
Pls assist

If you are reading code 208 on your PanelView, it does indicate that the PanelView cannot communicate with the PLC. Check your 5/04 for a red (flashing or solid) fault light. Try to go online with your 5/04 and see what the fault code is in your CPU. If the CPU fault light is solid red (not flashing) and you cannot get online with the 5/04, you should call AB tech support, as this could mean the 5/04 has a fatal hardware error and would need to be replaced.