Grief is complicated, and two years is no time at all to recover from the death of a parent. It makes complete sense that watching something you associate with him would still be painful, and there's nothing to be gained by forcing it.

Eventually you'll reach the point where reminders of your father bring up happy feelings, with the pain of losing him still present, but not overwhelming. That won't happen fast, but you will get there. That's the time to give TNG another go, and see how it makes you feel.

Hang in there, friend.