check your fla's file size. if it's zero, you can't do anything with it.
if it's not zero you can rename to a rar and use winrar to 'repair' it. that seldom works but if it does, rename to a fla and it will open.
if that fails, you can unrar the renamed fla and possibly recover some of your work.
if you have a working swf, decompile it to a working fla using a decompiler. imo, sothink's is the best.
and in the future, save your fla's with appended version numbers so this never happens again.
Thank you! Repairing the files didn't work, but I was able to decompile the swf. All of my images are renamed to numbers instead of my file naming system I had, but that is easily remedied.
I am now backing up to three places every 30 minutes.
when you back up, make sure you use a different name, with each back-up.
eg, when i have a project named handbook, i use handbook_v01 for my first save. then handbook_v02 etc. that way if handbook_v34 is corrupted, handbook_v33 is still good and you only lose no more than 15 minutes of work (assuming you save at reasonable intervals).