After that, i could upgrade to 2.00b11 and a battery symbol was always on on the screen. I'm ussing a PC power suply, since the mains Rio sent to me was an american one.

In your particular case, this could possibly be the root of the problem. It might be disk drive cable trouble, but it also might be the power supply. Maybe your scrounged power supply isn't giving the player enough juice for the hard disks to spin up. Please see this FAQ entry for the necessary specifications of the power supply.