Mac didn't turn on

Today I opened my mac as usual, and put my personal password but it didm't pass to the secretary.. it stayed all the time in the users part.. It didn't start! It Just didn't go to the desktop as normal. I tried everything but didm't work! Then it switched off, and never turned on again.. Just when I did SMC it worked, and now it functions normally.. What could have happened ??
Thank you!