Did you look at the score breakdown from your PR test? Was it even across all/most section types, or did one or two sections really bring you down?
The first step would be to know what's getting you more...the question types or the test as a whole. Review the answer explanations from the test, and log the errors in a spreadsheet. Look for patterns, see where you're going wrong. Then just work on one question type at a time, using the OG. Work through each weak area before taking another practice test.
Also, compare how you do on answering questions correctly when it's untimed practice vs. taking the test. If you do better when it's untimed, you'll definitely need to work on test-taking strategies (the PR book is actually good for this; you just need more practice with the strategies). If you're getting the questions wrong in both practice and on the tests, then you need to focus first on fundamentals.
And yes, you can reload the GMATPrep software and get mostly new questions, but retaking the test again and again isn't going to raise your score. You need to understand WHY you're getting the questions wrong.