Under the SharePoint lists, calendars and RSS feeds tabs there is also nothing listed. When going to File \ Office Account (the 'submenu' option above "Feedback"), there are two services listed under "Connected Services": one says "OneDrive - <his school's name>", the other "Sites - <his school's name>"; these represent both his problematic OneDrive and his school's SharePoint site. There's no way to remove these services; I can only add new ones. His school apparently has everything locked down pretty tight so the kids can't mess it up
When going in an unsandboxed Outlook to the "Manage rules and alerts" setting, then selecting the "Manage alerts" tab, and finally selecting the exchange account, Outlook locked up completely though, and after a wait of a minute or so a prompt appeared that there was "an error connecting to the OneDrive location" or such, after which dismissing it nothing further happened and Outlook was frozen... Killing Outlook and doing it again, the 1-minute wait is still there, although it pulls through this time, but now there's graphical garbage under the "Actions" header. Further evidence that OneDrive is linked in tighter to Outlook than you'd expect, and messing up the link breaks things.
Uninstalling the problematic OneDrive for Business (groove.exe + possibly msosync.exe) is unfortunately not possible on this laptop. It had the regular 'personal' OneDrive installed (onedrive.exe), but that one was configured correctly and caused no issues. I already uninstalled it nonetheless during my trials to get OneDrive working, since logging in to his account on office.com in the browser and selecting "sync" from there under the OneDrive tab caused his school's business OneDrive account to get linked by his personal OneDrive, messing things up even further. The remaining OneDrive for Business version is the one that's borked up, but that one is part of the default Office Pro install, and there is no way to alter the separate components to install/uninstall for that, since his school's IT locked the configuration (it's an all or nothing Office Pro install, and there's also only a Repair option and no Modify under programs & features). Killing all OneDrive-related processes from Task Manager (onedrive.exe, groove.exe and msysync.exe) and then starting Outlook again doesn't reload them, but Outlook under Sandboxie still misbehaves the same way. Wrestling some more with his OneDrive I got a prompt to appear offering me to use and install the latest version of OneDrive, but that only installed the personal one again and linked his business account to that one. The problematic OneDrive for Business was then still there asking for attention and Outlook still won't work, so still no fix.
I think the conclusion for now is that Office has become too complex and that if something somewhere goes wrong it starts doing unexpected things and it all falls down like a house of cards... I'll first let his school's IT department fix his OneDrive, and then let's hope this also magically fixes his hanging Outlook. Continuing solving it like this is probably just a waste of your and my time...
