First off, the obvious question. Are you sure you are using Powerprep and not something else?
Second, you can get explanations from the Powerprep software. However, you have to review the test immediately after you finish it. You cannot end the test, close the application, and then come back to it.
A screen will ask you to Proceed or to Review.
If you click Proceed, you exit the test. You can come back and see what answers you entered and what the correct answers were, but you do not get the explanations.
If you click Review, you can select specific questions to look at in each section. You see the question, the answers choices, and your answer. The button that says "Correct Explain" will explain the answer to you. Then on that new screen you have an "other explain" button that tells you why those answers were wrong. Again, after you are finished and you exit the test that's it. You can't get the explanations back. So screen print them if you want to refer back to them or copy them down.
Hope this helps.