I'm not sure that I understand what you're saying, so if this response seems way too stupid, please ignore it.
The best way I've found to view all the flights is to select 'Reservations' under the Links on the left side of the screen (just below where you log in your SkyMiles #). This brings you to a screen that's also used for one-way and multiple-leg trips. Select your dates/times and at the very bottom check the box that says "Specific times" and then proceed to the next screen. This will allow YOU to choose the specific flights you want, at the time you want (and check out the seating availability before you book).
See if your return flight shows up now. If not, it may be time to call Delta. It looks like they've cut some of the direct flights in the Hartford area, starting in May, and they've made other cuts across the country. Yes, they should be contacting you if that's the case, but maybe haven't gotten to it yet.
More likely, the flight is pretty full and the price is high, so it's not showing up when you type in the dates on the front screen. (Delta automatically selects flight combinations by lowest fare, so if the price of your return flight is high, there will be other flights displayed first.)
