Did you open Outlook after restarting the computer and get a message asking about Trusting an add on? You need to say 'always trust this provider' or 'trust this time'. Not the exact wording. The third option is 'deny or no this add on'. This add on is the key to the sync across Outlook and iCloud for Mail, Calendar, Contacts and Tasks.
If you did not get this question, check to see if the add in (iCloud App Add in) is listed in your add-ins as Inactive. If it is not there, then your install of iCloud for Windows did not finish or some other problem that you'll have to figure out there. You may need to install it again. Your firewall may be blocking but the next notes are the more likely essential to for a successful install.
The calendar and contacts set your want to sync with Outlook need to be selected (checked) in your iCloud.com.
Also important is sharing and making sure you've closed iCloud.com while the update runs and all the changes take place: GO TO iCloud.com check that you are NOT sharing the calendar and contacts. then log out of iCloud before installing the iCloud for Windows 5.1.
Always restart the computer after every install. Make sure Outlook is closed during the install of the iCloud for Windows. Do not open it when the computer restarts after the install of the app. the APP should open during the restart so you can check the options and APPLY them. Then close iCloud. Open Outlook, expect the question about trusting the add-in - iCloud APP Add-in. There is a blow by blow instruction in the supporting page for the download.
I hope this is some help to you.
BWWIGGs, TigerWizard