At the management level, you know that there will be projects doomed to failure. Knowing when to throw in the towel versus knowing how to give CPR is the skill that sets you apart. These are the three methods experienced project managers (PM) use to turn things around.
Review the Project
If assuming a point position after the project has hit a snag, the PM will typically arrange meetings with the former lead manager. This often gives insight into where things went wrong and allowed for a starting point from which to move forward. If that is not possible, the experienced PM will go back to the very beginning of the project, looking for the exact point things began to go sideways.
Put Together a Problem Solving Unit
Gathering resources from outside the group and sometimes, if called for, outside the organization, may be the only way to get the fresh perspective needed. Whether from within or outside of the group, it is important to have team members that aren't sunk in their investment of time and therefore resistant to make the drastic changes that are sometimes necessary.
Restructure the Team
If there were personnel issues such as clashes of temperament or personality, this might be all that is needed, to get things back up and running. An experienced PM will start by evaluating the individual team members strengths and weaknesses. It is important to change the roles of the individuals to ones in which they will perform the strongest. It doesn't have to be a morale buster if handled with tact; the team members will likely feel more valued and confident in their new role.
There will be occasions with the project has to be scrapped and started over. However, the best chance of succeeding is by utilizing the human resources and assets to their best ability. Often by having fresh team evaluate the situation, or allowing the existing team to take a step back and reassess, the PM will be able to salvage the project and reestablish the workflow.