This has happened to me before; so what do I do. I take a break to clear my head. I had a case once where I needed to find an important witness in a false arrest case but I kept running into dead ends. That all changed when I brainstormed with another investigator. Doing that helped me get another perspective once that happened I started making some calls and bingo I found a key witness. In this case no one knew the witness existed but by looking for another witness I found the key to my case.
Dead ends do not have to be the end. I take a dead end as an opportunity to regroup and reroute the direction I may be going in a case.