Which version of Office are you using? (2016? 2019? 365? Something else?). Whichever it is, my instinct would be to go through the 'repair' process for that particular software. (I can find the instructions for you if you wish but you'll probably find it simpler just to google 'repair office 2019', or whatever).
The very first thing to try though, if you've not already done so, is the old trick of 'turn it off and turn it on again' with your computer. It's amazing how often that works!
If you're still getting nowhere, try opening your files with different software, with LibreOffice Calc and Writer being worth a try with your Excel and Word files, respectively.