imposible to change ntsc to pal resolution

For an unknown reason, my mac mini has decided that my monitor is now ntsc, and everything is terribly ugly.
Fonts and colors are really bad.
Only things I have done is conecting through mini display port or hdmi. display port for monitor and hdmi for TV.

Anyone knows how can I force mac os to PAL refresh? Why has it decided to change?
Software is up to date.


Thanks