Thanks for your reply Carlok.
None of the possibilities apply mentioned by you as I have changed nothing.
While I was waiting for reply, I started a print with build plate temperature set at zero. I got this idea from another thread with same problem.
It worked and printer started printing without rebooting, except there was no proper adhesion to build plate obviously.
It seems that the power supply module is the culprit. I am contacting my supplier, hopefully they will replace it.
Regarding the configuration changes, I can not do it myself but I will ask my son. He is a software engineer.
Thanks again.