My first question would be... Did you format the hard drive? Or do you have your system set up on different partitions?
If the part of the file you were downloading is on another partition (still there) and the site allows a resumable download then you should be able to resume the download - by downloading again pointing to where the incomplete file is

..
If the incomplete file was lost with the reinstall (or crash) then you will not be able to resume it because there is nothing to resume
