Hello and thank you for choosing JA.
Typically Excel will do an autosave, every couple minutes or so, unless you changed that. It is setup that way by default, to autosave every few minutes.
If the screen went grey, then the Excel program, or windows itself, has become unresponsive. You can....A) wait for it to respond. B) Manually close the task, and restart.
If your system becomes unresponsive, and you HAVE to close it....and the file was NOT saved.....unfortunately the file is lost.
This goes back to the OLD adage....Save OFTEN, and save to a backup. The auto-save feature was developed just for this reason, and is turned on by default. But only came about in later versions of Excel, starting with 2007, I believe.
Here is a web link that has some instructions about autosave, and some other things tolook at in excel.
Come on back if you still have questions....and post them here.