If you're lucky and saved the file as a PDF compatible file (by default), you can try to open it in Acrobat then re-save it. However, if you re-save it, all AI specific features will be lost and you will only have the plain vector work.
You could try opening it in CS5 (download a trial), or you could reinstall AI.
These are the tips I have. If none of them helps, at least you get some hardcore experience to re-create the whole thing. (That's my idea of having fun...)