a) The point of a usb is to play songs off of your card and your card only. From what you're saying, it seems like someone has hacked your machine and put on songs prior to this. Songs from your card do not stay on the machine after you play, they load off your usb and only "appear" when you have loaded it for a round.
b) Songs loaded off a usb do not play music previews, this is just the way r21/r23 was made.
c) In order to play songs longer than 120 seconds, you will need to use the OggLengthPatch, which "tricks" the machine into thinking your ogg is 1:45 when it really isn't.
I highly recommend you read everything here, seeing as how nearly all of your questions were answered in it.
















