I've found the problem... Only one missing configuration at Settings of my Playbook! 'Sharing Files' was OFF! I switched to ON , and finally got access to the tablet, been able to copy lots of files (hundreds of pictures my husband took!) thru wi-fi. I didn't try USB connection, although.
I may return after to setting of my router and bind PlayBook IP address, in order to prevent have to change its IP number whenever it reconnect through wi-fi!
(Just one little errata: Dolphin is the default file manager of KDE, not Mageia, which features others Desktop Environment options, such as Gnome, LXDE, etc! I myself, still prefer to use KDE (by now...), besides it might be heavier than other DE options..!)