Well, what were the circumstances of the crash? What was the computer doing?
How do you know that the amount of data on the drive hasn't changed?
Were your files on the same drive? Or maybe a different partition on the same drive?
If you open up the C: drive, you can roughly account for the data on the drive by right-clicking on each folder in turn and selecting properties. You will see how many files and folders there are and how much room they take up.
Obviously the Windows and Programs x86 folders will account for a lot and there is a hidden folder called Program Data that could store a lot of data too but, if you open 'Users', you can check to see how much data is being stored in your Documents folder by right-clicking the folder that is named after your account, usually your name, and selecting 'Properties' again.
How much data is there in your folder? How many files and folders?