I'd try what Brad posted for Fallen Enchantress. Should work just as well for Sins: Trinity if it's not downloading correctly:
https://forums.elementalgame.com/434672
I'd also recommend turning off any anti-virus during download/install, as it may lock the file.
I tried everything form above ^^^ to reinstalling, re-downloading (thru stardock), windowed mode, texture change, disabling intro movies, to no avail. Haven't heard back from support yet. I can't figure it out.