You need to ensure the new PSU is compatible with this board and many new PSUs these days are NOT suitable for very old boards such as yours because they have connectors which are unsuitable and/or the current capabilities for each rail aren't balanced according to older ways of going about things. Older boards tend to require more on the 3.3 volt and 5.0 volt rails whereas newer PCs need more on the 12 volt rail(s) - this is reflected in the changing ATX standards over the years. If you are sure your PSU is suitable for THIS board, you could try unplugging mains from the PC and removing the coin cell battery for a while then reinstall and try powering up again.
What symptoms was the PC exhibiting prior to the flashing green LED - was it unreliable at starting?
Thanks for Answer,
before flashing of LED i just installed thermal printer it works fine for 2 days, but user complaint me that the printer is not working it shows the USB Device is not Recognize, to overcome this issue i was re-installed driver & but issue is not solved, to check this issue i was disconnect power supply of thermal printer & start again. as soon as i power on the thermal printer my pc goes down & then it shows the LED Status is Flashing & no display. so i test the thermal printer on another pc it creates same problem on another pc as soon as i power on thermal printer pc goes down but another pc will restart normal i restart the PC so i replace the USB cable of thermal printer it works fine, but my previous board is now not working so replace the PSU with new but now status of LED is changed from flashing to continues LED but very poor & still no display. can thermal printer cause my board is dead?. Please help can my board is dead or some another procedure to recover it. i was tried everything as you explained. but no works.