Thanks a lot!
If you're stuck at character selection(single or vs), restarting the game should fix it.
If you've entered the selection screen, try not to press pause and return to main menu. The game tends to get bugged upon re-entering that screen.
If you want to get back to main menu, you would like to do this instead:
Enter a stage > pause > press A,B,C at the same time. This will reset the game properly. Or you simply restart the game.