Whether its GMAT Prep or Power Prep, your score is within 470-540 range. If you see your Q and V breakout, the scores are pretty much the same.
The lower the GMAT score, the volatility is greater and higher the GMAT score, volatility is smaller - meaning that as your GMAT score rises (i.e. - 700 range), it is much more difficult for your score to vary. That's why it is so much more difficult to raise your GMAT score in 700 range - compared to GMAT score in 500 and 600 ranges.
My recommendation is that you focus on verbal section to raise your score. Many GMAT takers that score low on verbal are usually international students.
To raise CR - use Powerscore CR Bible. It is a long read but it covers every topic.
To raise SC - use
MGMAT SC guide. It is simply the best.
To raise RC - try using GRE RC guides...they are very difficult and very good in raising your RC scores.
Try to master easy questions first before attacking more difficult problems. This is because GMAT CAT will give you easier questions first and once you get those right consistently, it will show you more difficult questions. If you constantly practice with 700 level questions, you won't raise your score because you will consistently get 500 and 600 level questions wrong.
Good luck!