reaction to power button

[George Shuklin]

Hello.

I'm fighting with my power button on desktop PC. I want it to suspend 
PC, but when I press it, computer shut down itself (gracefully). When I 
switch mode to 'ask' in xfce-power-manager, it displays question and 
still shutdown.

I think something interfere with xfce-power-manager, but I just can't 
find what it is. How should I debug this?

Please help. Thanks!