Please Watch This 2 Minute Tutorial Before Downloading And please make sure your java is up to date.
If you already tried to run the client before putting cache in the C:\ drive, you need to either delete the Deathlypvpz V3 folder in the C:\ drive and then drag the folder from the .zip file into the C:\ drive OR when you copy the folder from the .zip file and are prompted, click copy and replace.