Plc omron cqm1-h cpu21

Hello all,
This is my first post on the forum and I hope somebody could help me, in factory we have one system for nitrating tools (furnace), and heart of the system is PLC OMRON CQM1-H CPU21,system existed since 2005,ok now problem is: before two days furnace stopped, message on the Scada PC was,cominication problem with PLC,all led diodes on the PLC turned off(RUN,ERR/ALM,INH,PRPHL) except diode COMM which is blinked, any outputs doesn’t work, from inputs we are have only auto/man (form double switch on the door).
We can’t to communicate with PLC over CX Programmer, we mistrust the CPU doesn’t work.
Is somebody having similar problem (according to symptoms) and what is reasons for that.
Thank you in advance.

What about PLC power supply.They tend to stop working?
The comm led flesh because the PC send message.

try disconnecting all wires from the PLC check and make sure the power supply is working also I've had a problem with the backplane of the PLC that caused a ground short. This may be a strong possible cause of why the PLC is not powering up. Also one quirk on Cx-pragrammer is opening the correct commport from when it was originally programmed at. Check what comm port your curently using goto the project tree right click the processor symbol and goto change and set the correct comport there rather than use auto connect

Thank you gays for suggestions, we still not sure what is happened, processor unit we have sent to a Omron service and we will see.
Thank you anyway