iCloud Preferences Frozen After Mavericks Installation

Once I installed Mavericks, the System Preferences screen for iCloud remains frozen in "loading" mode with the sunburst spinning. Most of the selections in iCloud are checked, and not accessible at this point. For two days now, have been unable to perform any actions in this window. This condition also prevents be from shutting down or rebooting. I tried letting the battery drain, but the system returns to the frozen process upon powering up. Other computer functions perform normally while this goes on. What can I do?