Barhar pretty much hit the nail on the head....you basically answered your own question. If your disk is full, then your disk is full...that's the problem. Either you have to get a larger hard drive, delete some files to make space, or you might be saving in a location that isn't the system hard drive (or some other destination you might think you're installing into).
Again, you need to be more specific as to how you came to reach this problem. Just saying "it said the disk is full" is still quite vague. Remember that we can't see what's happening on your computer so to assume that we would know the answer from your vague descriptions is wishful thinking.