Excel starts minimized or with smaller size window
Erase the following registry keys to get it to reset.
Replace 16.0 with whatever version of Office you are running e.g. 14.0, 15.0, etc. Office 365 uses 16.0.
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Excel\Options Pos
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Excel\Options Maximized
Deleting these two keys with Excel closed will force Excel to recreate the keys, which will resolve the issue.
Why do all my Excel 2016 files open to the size of a postage stamp? - Super User