All LED Flashing Simatic S7 400H CPU

There are 2 stations (1 operator stn & 1 Eng stn.) for PSA system. Operator station was out due to hard disk failure. It was made healthy by installing new hard disk & subsequently installing the software required like winCC, simatic manager for taking the PC in line. But after activating the winCC, the communication was lost & all LED's of both CPUs of PLC started flashing. Plant was non operational during that time. It was normalized by reseting the power, but the cause of such phenomena is not not identified. Diagnostic buffer is also not showing messages on that time.

What might be the reason for such event?
Yes, it was discussed with siemens engineer, but they also do not have firm root cause of such event. They have recommended to upgrade the firmware version.