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A possible resolution from Apple's dev. forums:

Apply Patch 14.4.4 from Microsoft AutoUpdate, then perform the following
1. Quit Outlook and PowerPoint
2. Head into ~/Library/Preferences (shift-cmd-G from the desktop)
3. Delete com.microsoft.outlook* and com.microsoft.PowerPoint*
4. Reboot
5. Start Outlook/PowerPoint
Outlook/PowerPoint should start up now, and ask to add a new account, but you can cancel this.
 
The solution which involves deleting the various preference plist files did not working for any of the 50+ people in my office. The only one which did work was tzubak's solution, the one I referenced from a Microsoft forum.

YMMV.
 
For me 14.4.5 still renders the list of folders oon the left in weird way - "Inbox" and "Sent Items" are in black but everything else is barely readable in grey.
 
excuse my ignorance but what does that mean?

After I set up Outlook, it kept asking for the password for each account, even though I entered it correctly each time. I also checked to make sure the passwords were saved properly in keychain. No matter what I had been doing, the popup would continue. I went back into keychain and did a repair. And for whatever reason, every email keychain had a problem. Once the repair was done, I haven't had the annoying password popup.
 
After I set up Outlook, it kept asking for the password for each account, even though I entered it correctly each time. I also checked to make sure the passwords were saved properly in keychain. No matter what I had been doing, the popup would continue. I went back into keychain and did a repair. And for whatever reason, every email keychain had a problem. Once the repair was done, I haven't had the annoying password popup.

got it, thank you!
 
After I set up Outlook, it kept asking for the password for each account, even though I entered it correctly each time. I also checked to make sure the passwords were saved properly in keychain. No matter what I had been doing, the popup would continue. I went back into keychain and did a repair. And for whatever reason, every email keychain had a problem. Once the repair was done, I haven't had the annoying password popup.

@BasicGreatGuy
Please could you say how you did the keychain repair - I'm having the same problem after installing 10.10 and updating MS Office for Mac to 14.4.5
I can't get any email, only the pop-up about the password.
Thank you :)
 
@BasicGreatGuy
Please could you say how you did the keychain repair - I'm having the same problem after installing 10.10 and updating MS Office for Mac to 14.4.5
I can't get any email, only the pop-up about the password.
Thank you :)

@BasicGreatGuy - problem solved! Thanks anyway for your post :)
 
My Outlook 15.8 wouldn't show the main window today, and the solution was to select View/Go To/Email (or CMD+1) from the menu. Then Outlook crashed and when I reopened it the main window was visible again.
 
thanks!

OK with Outlook 2011 14.5.0 150423 and Yosemite 10.10.3 I believe I had similar behavior (open up all the exchange "expand tree" folders, close exchange, main window refuses to return *ever*).

Tzubak's solution worked for me (thanks!)
The one note I'd add is that for me, if I switch to the new identity and open outlook, if I play around the folders a little before exiting and switching back to my main identity (for instance, expand "smart folders" then close it) then that seems to help even more consistently, FWIW.
 
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