Cant download

i was reinstalling SL and when i was retrieving the download it would go to 40 sec left then it would start going up so like 20 sec later ti would say it was done so when i click run it says it cant download it because it could damage a disk or something i tried defragmenting it and it still wont work , any suggestions?

Just re-download it from the download page.

http://secondlife.com/community/downloads.php

Also make sure you aren't low on disk space, so you'll have enough room to download it as well as some room to run the install.