All my account preferences are greyed out

I have an iMac running OS X 10.9.4. I cannot sync Calendar, Reminders and Notes between iCloud and the Mac. If I open the Internet Accounts pane in System Preferences, all options are greyed out. Similarly the iCloud mailbox in Mail says it’s offline and refuses to go online. If I click Edit Account Information the incoming mail server is mail.example.com and can’t be edited, yet if I input my login details it accepts them. If I go to the Safari iCloud app all the apps are synced with my iPad, iPhone and iPod – but not the Mac… Anthony Leeds This is likely a preference corruption. Have a look at iCloud preferences. Are the checkboxes for each app greyed-out there as well? If they aren’t, try unticking Mail and ticking it again. That will force it to run the auto setup procedure for your Mail account again. If the boxes are greyed-out there as well, try signing out of iCloud and signing back in again. If this doesn’t help and the ‘-’ button in Internet Accounts preferences is greyed out, so you can’t even delete the iCloud account, you may have to delete ~\Library\Mail\V2\MailData\Accounts.plist. Reboot and you should be able to recreate your iCloud account in Internet Accounts preferences.