A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
The usual issue are columns full of formulas that doesn't calculate anything.
Go from sheet to sheet and press CTRL+END to jump to the last used cell. If you can't see your data from that cell scroll up / left till you see it, select all rows below you data till the end of the sheet and delete the rows. Do the same for columns.
Locate and reset the last cell on a worksheet - Excel
In most cases, this will significantly reduce file size/load time and file behavior will return to normal.
Andreas.