What operating system are you on?
If you are on ctree or btrieve it could be that you have run out of hard disk space. If you are on SQL 6 it could be that you have run out of locks.
How long did you wait? Sometimes these things just take time.
Did you check the windows task manager to see if the processor was still in use? Don't look at the Dynamics not responding thing. It might not be responding because it is busy doing the year end. Check to see how much the processor is being utilised. If it has crashed then this will be around 2%. You shouldn't be running any other applications on a workstation that is performing a year end.
Year end processes can take some time I have seen some take more that a full day to complete depending on the number of transactions you have in your database, the operating system that you are on, the power of the workstation and the speed of the network.