Do you still have the microphone selected as one of the audio sources on the Recorder's main window? (directly under the Record Sound option))
FlashBack cannot record sound without the appropriate sources being selected and enabled. If you are recording a meeting, you will want to have one source for your microphone (to record you) and one for the PC speakers (to record the other participants).
Yes, all of the boxes, if you want to record the microphone and the PC sounds.