Torrents work by downloading little bits of each track etc in no particular order so you probably haven't got a full track yet.
You'll have to wait until they (ie the full torrent) finishes downloading before you can play them.
When you look at the files, they appear to be complete but that's only because, while they are downloading, your PC has allocated the required space.
They'll be fine one fully downloaded.
As jasonflz says, there's no way to speed up a torrent.
