How to Safely use MS Office for Mac installation disc without Data Loss

I overdid removing suggested files using CleanMyMacx to make space on my ageing mid 2011 iMac. I had MS Office 2011 on my machine but after all these years I continued to use only the Excel and Word part of this software. After my zealous removal of suggested files, I cannot enter new data onto Excel or new documents on Word without both quitting unexpectedly. Obviously, my efforts to make space on my Mac is the cause of this.

My existing Excel and Word files are on my machine; I haven't lost anything but I can't add new data to either of them. What can I do about this? I have the original MS Office for Mac installation disc but can I use it without damaging or removing existing data? I was advised to create a 'guest user' and install MS Office to test that my machine could take it. It was succsfully installed for this guest user part of my machine but old and new compatability issues got in my way of a satisfactory outcome. Your help and advice would be greatly appreciated.

[Re-Titled by Moderator]