Assign a libname to the Excel workbook and use PROC CONTENTS.
*This code will create a libname reference to an Excel file and list all Sheets in the results window; libname sample xlsx 'C:\Temp\Sample_v2.xlsx'; *your statement will depend on your OS/Excel version;
proc contents data=sample._all_; run;
*copy all worksheets to work library; proc copy in=sample out=work; run;
What do you mean it keeps loading? Which step is it having issues with? Run each section (libname, proc contents, proc copy) separately and see exactly which one is problematic.