If you saved in increments as you built the scene with different file names, try going back to an earlier version and open it. Try to save it under an new file name.  If all is okay there, I suspect you are working with a corrupted file.  Or possibly you have pushed the memory capacity to its limits and the save process is taxing your computer beyond its capabilities. 1 gig of ram isn't very much when it comes to 3D graphics.