Simatic rack pc communication fail frequently.

Hello guys,
Our plant we are using simatic rack pc for scada system. We purchased new simatic rack pc from vendor and try to fixed but we observed it is communicating with plc and working fine and after few hours we see warnings message that many time message came No communication with plc and Visu computer(scada computer). When it is communicate and ethernet led light blinking and sometimes ethernet led blinking stop and plc CP side Txd and Rxd led also going stop and this time we are facing No communication plc and Visu.
Now we are are using our old simatic rack pc. It is working but sometimes Fan and temperature fault occurred but still it is working good.
Now my question is what could be reason for communication fail plc and Visu computers.
I replaced ethernet cable and fixed new ethernet hub but no result.
If any one have any idea please support and guide me.
Kind regards.

Do the old and new Simatic rack pc's have the same IP address?

Is there any chance 'something' on the network has the same IP address?

Poet.

Dear poet,
Thanks for support. We are using two simatic rack pc in same place. One for visu and other one for prisma.I received pc from vendor and I don't check it's Ip address.
As far as I know vendor make ready and supply to us. OK I will check and inform you.
Kindly note that if any computer fail we can run both program in any one computer's.
Kind regards.
Uj