I understand that you have baselined the schedule. As and when you re-baselining an existing schedule i suggest to proceed as follows.
Step 1; Go to MAINTAIN BASELINE and create a new baseline. You have two options. The first one is to create an complete new schedule and the second option is to create an new baseline in the same schedule. Be a little patient but it takes usually several minutes. When the baseline has been set give the baseline a name say, BASELINE12/12/12. Also make the BASELINE 12/12/12 your PROJECT BASELINE. this is at the lower part of the same form.
Step 2: Go to ASSIGN BASELINE and assign the baseline BASELINE 12/12/12 as the project baseline.
Note that MAINTAIN BASELINE AND ASSIGN BASELINE are two different tabs.
The reason for this is that the software allows you to select the baselines you would like to compare the current schedule and the baseline you select. In you case you would probably use the original baseline from the approved schedule until the next baseline has been approved. But suggest to use the new baseline 12/12/12 for updating of the schedule so that new activities can be properly monitored.
Step 3: Go to View bars and select the tick box for PROJECT BASELINE.
You should now see that the PROJECT BASELINE bar is displayed , usually in a yellow color, under the green colored bars.
So in short, maintain the baseline, assign the baseline and display the baseline.
Trust this is clear.