iMac G5 won't sleep

[SergioDeNice]

Hi,

So I've got this A1144 iMac running Sorbet which won't sleep, whatever I tell it through the system preferences.
I tried resetting SMU and zapping the PRAM but to no avail.
What should I do?
TIA

Serge

 

[SergioDeNice]

I must add, it goes to sleep without any problem via the apple menu.

 

[SergioDeNice]

No one?