I have the 2007 home/student version, that operates with Microsoft Vista.
Every morning before I open the file (and its been two weeks since I've
backed it up)...I change the date on the file...so today I made it "SA Client
Outreach 10.10.07"...

When I opened up the file, it said this: The file you are trying to open,
'SA Client Outreach 10.10.07.xls', is in a different format than specified by
the file extension. Verify that the file is not corrupted and is from a
trust source before opening the file. Do you want to open the file now?

It then gives me the option of saying "Yes, no, or help." If I click yes,
it opens the file but its blank. The file itself was massive, but it now
says that it is 0 bites.

I have no idea how to recover the file, or what happened to it. Its as if
it just vanished into thin air.

Do you have any idea what I should do, or where it might have gone? Any
assistance you might be able to give I would really appreciate.