Dishwasher leaks water but doesn't work?
The dishwasher should drain into the disposer so it sounds like you have a combination of 2 problems:

1) significant blockage in your sink drain p-trap that is causing water to backup into the dishwasher (path of least resistance). However, it still shouldn't leak normally.

2) the DW drain wasn't done with an air gap or high loop that prevents #1. In other words, the drain hose should run out of the DW, then much higher than where it connects to the disposer before dropping down again to enter the disposer.

That doesn't answer why it is leaking though. Poor drain connection, bad pump, bad seals. If it leaks that bad, it may be a blessing it hasn't worked.