If your tstat is disconnected then it certainly won't run
Are you sure 240v power is available? You can check this with a meter, but if you're not sure how to use it DON'T TRY TO DO THIS. You can hurt yourself badly (or worse).
Some of these units have circuit boards with 3 or 5 amp automotive-type fuses on the boards. You might look on that board to see if the fuse is blown. If it is, then TURN THE POWER OFF, replace the fuse, and start it back. If it immediately blows again you've got a short, and you'll need to trace down that short. If you're not sure how to do that, you might consider calling someone to do this for you.