Outlook Fails to Start - Trying to open profile

Brief History.

• Outlook working fine
• I found OneNote wasn't syncing some pages, it turned out to be an issue with AVAST but whilst trying to solve the issue I logged out of OneNote. Turned Avast off, logged back into OneNote and syncing now working.
• Opened Outlook and got a message asking for a password for one of my email accounts. In a rush so just closed the login dialogue. I may have closed outlook at that point.
• A few minutes later tried to open outlook and it hangs trying to load the profile before erroring with 
• Outlook wont open in safe mode.
• I have tried:
  • rebooting PC
  • running outlook as admin
  • Quick Repair
  • Reset Profile XML file - outlook.exe /resetnavpane
  • Delete Profile XML file

After lots of messing around Outlook suddenly but briefly opened, but is now not working again.

Whilst it was opened I managed to compare the .OST Files and settings to those I have on another PC with the same Outlook email accounts.

There are 5 email accounts, all IMAP/OST but I notice one account on the problem installation shows as "Exchange" rather than "IMAP", also this same account is "Default" where I expected a different account to be default.

The laptop was new a month ago and has worked fine until today, any thoughts?