Hot/Neutral Wired Together?
Cable #2 is a switch loop, so try turning that switch on
What you see here is the origination point of an old-style switch loop that controls a receptacle.  Cable #1 feeds power from the breaker onward to some other box, so we can ignore it and focus on cables 2 and 3.  From that white-wire-to-black-wire splice and the fact cable 2's black is spliced to the always-hot black, we can tell that cable 2 is an old-style switch loop, carrying always-hot to and switched-hot back from an ordinary light switch somewhere.  Cable 3, then, feeds a switched receptacle with the switched-hot from the switch loop, as its neutral connects into the main neutral bundle.
As a result, turning the switch at cable #2 on should get your receptacle to work.  While you're in here with the breaker off, there are a couple things you can do to clean this box up for the next person working in it, though.  First and foremost would be to use black tape or Sharpie to remark the white wire in cable #2 as a hot wire; that way, it's clear that it's hot, not a neutral.  Furthermore, Code says that that white wire in cable #2 should be carrying the always-hot down to the switch, with the black wire in cable #2 used to carry the switched-hot back up.  Once you have the relabeling done, swapping those two wires around should be a simple matter -- once you're done, the relabeled white wire from cable #2 will join with the black wires in the incoming feed and in cable #1, while the black wire in cable #2 connects to the black wire in cable #3.
Note also that since this switch loop controls a receptacle, it's exempt from the NEC 404.2(C) requirements for bringing neutral out to the switch location.