installed new disposal and now dishwasher will not drain
Seems likely that the knockout plug in the drain line on the disposal unit needs to be removed. (It's there for people that aren't connecting a dishwasher.) User Fiasco Labs likes a drift pin and a hammer; I've used a socket on an extension and a hammer. Either way, make sure you don't leave any bits behind.

If that's not the root cause, comment back and we'll do our best to sort you out.