What do I do? Thank you
A quick search on Google for that error message leads to:
.XLSX PROBLEM - Failed to Connect to Database - Class Not Registered
Error: Failed to connect to database. Class not registered
...and many more such links...
So basically, just Download and install the 2007 Access Databse Engine driver and this should fix the issue. Try this link:
The fix for this is described in the help, along with other guidance for using Excel data.
If you are using the current version of Office you should install the 2010 driver, not the 2007 one. It is linked in the help:
Understanding how to use Microsoft Excel files in ArcGIS—Help | ArcGIS Desktop
Alternatively, you can save as .xls or .csv, loading those does not require the Excel 2010 driver installed to load to ArcMap.