If the file opens at all in CD X3, try this-
Try exporting the file to .eps format, then re-opening it. Unfortunately, you'll lose a lot of Corel Draw' goodies, but it may save some hard work.
I have the same problem once in awhile. I started on CorelDraw8, then 11 and now X3. I haven't been able to correlate the problem to any specific version.
Occasionally (rarely), I open a file in Corel Draw X3 to find just a blank screen. Opening the object manager shows the objects are there, but I can't add attributes like color, line thickness, etc. no matter what I do. I tried saving the files to previous versions, copying objects to a new page, etc. The only thing that got back any of my data was the export to .eps and reopen. Not entirely satisfactory, but better than starting from scratch. I'm mostly in the sticker business so I've never tried to recover colors.