Eddie, Critical path depends on a couple things. In your File > Options > Advanced window, at the bottom (Project 2013), there is an option that defines what Project considers as a critical task. The option is “Tasks are critical if Slack is less than or equal to…”. This option means that you can decide that tasks with 1 day, 3 days, or 0 days (whatever value you choose) are considered as critical.
With that in mind, add the Total Slack column to you view table. Chances are your total slack values on each task exceed the value you have in your “Tasks are critical…” option.
Additionally, Project has a difficult time calculating critical path/slack if the project tasks do not have dependency relationships. If you’re familiar with forward/backward pass concepts used to calculate Slack, then you’ll understand how breaks in the dependency chain will impact Project’s ability to calculate Slack values. So verify that your tasks all have dependency relationships and that there are no dangling dependency chains that have missing predecessors at the front or successors at the end of the chain.