Ok the problem is that my dad gave me his laptop to clean off all the data on it so it'll be as if he just bought it, but the only problem is that I did that and it still only has 50 GB left on the 320GB HD. Before he gave it to me he had a Vista OS and now has a Windows 7, and he told me that he gave it to a guy to fix it for him and he says that he cleaned it up for him bout it is how I first stated.
If you want to set up the laptop as it was before, meaning no other files on it, just re-install Windows 7. This is if you don't care about the installed programs and any saved files on it, which is what "clean off all the data" usually means.
During the Windows 7 setup, go to advanced drive options and delete the partition. That will wipe all the old data. Keep in mind anything on the drive will be gone at that point.
I have tried Windirstat on my desktop and it worked wonderful and now that I have received the laptop once again I shall try using Windirstat and also TreeSize Free in the afternoon. If all else fails I will resort to re-installing Windows I shall notify on the progress once I am finished.