Critical task bars stopped turning red

willard800,
Did you add any new Gantt bar styles (Gantt Chart Format > Bar Styles > Format)? If so, it's possible the new bar style is overriding the Critical bar style. If that's the case, you'll need to re-configure the bar styles list so the bar style for critical tasks is at the bottom.

It's also possible the Gantt Chart view is corrupt.
1. Switch to another view (e.g. Task Sheet)
2. Go to the Organizer > Views tab
3. On the right side selection list, select Gantt Chart and then, Delete.
The Gantt Chart view will then revert back to the original Global Gantt Chart. Does the problem still exist?

It could also be other things but let's see what the above yields.

John