help with galaxy S2 nook

ok, I havd a very basic computer knowledge. I have used nook for the last 10 years because i could keep all my books in my computer named in ways that i could keep track of series and sideload them into the nook. I bought a galaxy S2 nook in feb. of this year. In the last week there has been an update on it and ever since I have not been able to open any of my sideloaded books. Just to read on my s2 I have had to diable the nook portions and download google play books. Can anyone give me direction on what are the easiest apps to use keep books organized and to read then.

thanks
carbeth