Q: Power-button is not working properly anymore. It is causing sleep mode!

Pressing the power button is a shortcut to make the display sleep.

Press and hold the power button for seconds until the dialog box appears.

I'm experiencing the same curious problem, here(Macbook Pro 13", mid 2009).  This started after upgrading to, Mavericks.  One press of the power button always used to bring up the dialog box with the various options.  Now, just a press of the power button, and it's immediate sleep time.  Music that was playing in iTunes stops playing, so it's different from the screen sleeping.

But, as dominic23 states, "Press and hold the power button for seconds until the dialog box appears", does seem to do the trick.  This is just a different behavior than in the past.

Thanks for the tip, dominic23!  Is this something new in, Mavericks?

This is new behavior in Mavericks:

http://support.apple.com/kb/HT5869

Thanks, Bradley Fol!  I'm resting much better now.  Sure am glad it wasn't a kernel panic of some kind! 

The problem I have, is that i keep hitting the power button instead of the delete key. I am clumsy but at least before i could Escape the problem, and in system preference, i could remove the option to Alllow the power button to put the compteur to sleep. I don't see why they removed it. Anyone has found a way to get it back.