Microsoft Excel command line switches

When trying to troubleshoot Microsoft Excel startup problems, it can be very helpful to utilize the command line switches at startup.

"C:\Program Files\Microsoft Office\Office\Excel.exe" /s

/s is safemode, Excel starts without any third-party add-ins

/r opens a specified file in read-only mode i.e. /r "c:\testfile.xls"

/o forces Excel to re-register itself. The registry key HKEY_CURRENT_USER\Software\Microsoft\Office\xx\Excel is rewritten
xx - 8.0 = Excel 97, 9.0 = Excel 2000, etc

/regserver forces Excel to rewrite all related registry keys and file associations

/unregserver unregisters Excel

Source and more switches: Microsoft Support kb291288