Well how did u restart ur computer?! If u just unplugged it from the wall it may have corrupted and deleted automatically, or it just wasn't a file that saves every some mb. If u restarted ur computer normally, did u pause the dl and exit lw first? Also check ur directory, the one where things go when their done, yeah go there and check, dont check in incomplete dl, that is very vague. And do u know if u had any viruses at the time?