Illustrator :: Design File Opens But Most Of Objects Gone

I worked on a design saving it about every 10 minites  and also saving a copy every hour. Later, when I try to open any of the copies of this file, Illustrator gives me this error:

the file opens but most of the objects are gone. I managed to open the file with Adobe Accrobat and saved it as eps then open it in Illustrator but the paths are mess and all effects converted to embeded images.I also placed the file but if I try to edit the link it gives me the same error and when I embedded the link it was a little bit better but similar mess like the eps saved from Acrobat..I'm using Illustrator CS5 Design file Windows 7.