All i want to do is run it as a file server for my media
You don't really need a "server OS" for that. You can just share folders to LAN, using Samba for Windows clients.
If you want a GUI, you might as well install Ubuntu desktop. By default, there is no root login (just sudo) and no ports are open.
If the machine has more than 4GB RAM, use the 64-bit version. If you want software RAID and/or whole-disk encryption with LUKS, use the alternate CD. If you don't like the Unity desktop, you can use Xubuntu or Mint instead.
and maybe run a little bit of hashing for litecoin on it,
I doubt that any used server will get a block during your lifetime.