One thing I've seen help is to open all of the parts first if that is possible. Another thing you could try is to move the assembly file to a new directory & rename your working directory so it can't find the parts on its own. Then open the assembly up & don't let it search for the parts. Then after opening it then open & look for each part from the feature tree of the assembly.
In the case the suggestion from the John doesn't work out, then please send the file to your VAR for diagnosis and fixing the issue.
I copied over all the files to my local hard drive (was originally accessing them over the network) and was able to open the assembly. I lost some of the last modifications I had made, but that's a whole lot better than losing the whole thing. Thanks so much for the quick advice.