Thank you very much Grant!
the machine was buyed as refurbished from shop, now after a while I saw this behavior(it was plugged since came here), so..I can't know if it has been off AC Power for a lot of time before I've buyed it...but it's possible. But shop isn't much "collaborative", they say "it's normal and with no solution"...incredible...
"'Where I am going is that' your parameters may have gotten clobbered"
-How can it be done?
"An PRAM Reset (assert command Option P R at startup and hold [seems like forever] through THREE sets of chimes before releasing) can fix that for the short run, but if the battery is getting tired, any interruption of AC power can cause wonkiness to get worse, and has even been know to preclude starting up."
Didn't know that...interesting, anyway, my mac does two chimes and then boot and the problem remain.
The battery seems to be the most interesting solution I've read since I am serching, thank you a lot!