QUESTION:
I've inherited a theme for a PowerPoint slide set and find that I am unable to insert automatic slide numbering. I've tried working with the Master Slide, moving and even removing nearby elements (images, lines, etc.) all with no luck.
Answer:
The problem is that the theme does not include the function of inserting slide number.
Here's the tutorial of how to solve the problem, follow the steps below (I'm using PowerPoint 2007).
1, Open your PowerPoint presentation, and click View->Slide Master

2, Selcet the first slide, and click Master Layout. You'll see the Master Layout window pops up.

Check the option "Slide number", and click OK. Then you'll see a new text box appear on the bottom of the slide:

Select the second slide, and check the option "Footers" to show the footer placeholders. Repeat this action for all other slides.

Close Master View.
3, Now you can insert slide number with no trouble.
Click Insert->Slide Number, and you'll see the Header and Footer window pops up.

Check the option "Slide number", uncheck "don't show on title slide", and then click "Apply to All".
Now you can see the slide numbers show up on all slides.
Note: You can change the slide number font size, color, and position at step 2.