a 400watt true rated PSU will do the job. however, kung generic PSU yan and tingin ko medyo matagal na rin yan, kulang na binibigay na power niya. I think its time to switch to another PSU. Kung generic parin kukunin mo, I recommend something like 500-600watts.
kung ragnarok lang kasi and other online games nilalaro mo kahit mag onboard video ka, tatakbo na yan dapat eh. so baka nga PSU ang problema