I am also having the same issue. I could not see any multiplayer options (1v1 2v2, 3v3, 4v4, and ffa) until I completely rebooted my computer, but I am unable to even SEE the 1v1 option. 2v2, 3v3, 4v5, and FFA are all there.
---- You have to WIN a co-operative game --- if you keep losing, you will end up only ably to play an EASY Co-op game. I had same problem. I think if you lose a couple in a row, your options become restricted.