Thanks for all your help.
Thanks Robblok, I moved the relevant files back from Onedrive to my PC (I hadn't realised that I had moved Outlook files) and it's now working again. Thanks.
Just one other question......
The Outlook that's now working again is the desktop version which is included in my Office 365 package where I have my own domain name etc.
My web version of outlook on my notebook (I have a @hotmal.co.uk e-mail address) developed an issue a few weeks ago. Any new e-mails that I receive instantly disappear. They don't go into my deleted or spam folders, they just completely disappear. However I can view them in the inbox on my outlook application on my android phone? Any ideas as to how to fix?
Thanks.