Two ways:

1.  Go to Edit and Genearl Preferences. Check the box next to "Launch to Factory State".  Click on Interface tab and check the box "Launch to Factory State".  Click OK. Close Poser and then reopen poser.  The Poser interface should be in it's default state.  Go ahead and reset your preferences.

2. Reintall Poser if the above fails.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi