.blend file no longer recognized by blender?

iv been working on a project for a long time, and yesterday, i saved my file, and then tried to render. for some reason my computer froze and i had to force shut it down. being very happy i had just saved, i re booted and tried to open my file again and it gave me an error reading "file format is not supported in file: C:\Users\Username\Desktop\Portal Pan.blend". is there any way i can get this to work? iv also tried restoring last session but it just opens the default screen. Can get i get it back or even get it back to a previous save?