Is this late in the game and do you have automated workers. Sometimes there is some wierd loops that automated workers get into late in the game. Hit esc and wait a bit see if the save/load menu pops up.
or
Hit return and wait a bit, the game may go on to the next turn.
If that doesn't work, then try activating a fortified unit at the beginning of the turn an don't re-fortify him, leave him active and hit return when you have finished your turn.
Late in the game, especially large games, I always leave one unit with no orders, the game never hangs on me. I know that my turn is over when it won't cycle past that unit and I end my turn with return.
If you still can't get past that turn, do a little time travel, go back a turn or 2, and un-automate your workers or leave a unit active with no orders.
