Here below are the names that can be used to name the Homepage:

Index.htm   
Index.html 
Index.asp
Index.php
Index.shtm 
Index.wml 
Index.aspx 
Default.asp
Default.php
Default.html 
Default.htm
Default.shtm
Default.wml
Default.aspx   

If you have index.htm, then index.html will not be visible automatically (as it is next on the list) and so on. Once you have chosen the name of the home page, you must check that there are no files with any of the other names.
For more information please consult the online guide on this page
vademecum.aruba.it/start/redirect/index.htm.