If you are extracting a very large .tar.gz file, the process can be terminated before it finishes. This can sometimes help:
Run the command again, but add the -k flag so that it will skip over any files that have already been extracted.
So if you were extracting sample.tar.gz, like this:
tar -xvzf sample.tar.gz
Then, after it gets terminated before finishing, run this (it has the -k flag):
tar -xvkf sample.tar.gz