just to make sure i put it correctly:
my keyboard doesn't turn off by itself or something, so is not a power related issue, but it gets frozen, and when it does, the sound/tone i use for right hand would keep sounding until i turn the keyboard off. no matter what else i (try to) do, it wouldn't help.
and also sometimes, as i said, the OS seems to have some bugs that would produce the "ultimate" problem: freeze the instrument when playing it.
i did upgrade to the newest version of OS, it was not necessary the smoothest thing, but nevermind... i thought the problems were solved, but obviously not all of them.
...and i am thinking now, maybe i own one of the first released E60 keyboards, which i assume are more predisposed to "childhood diseases".