Sounds like my problem... It's PROBABLY your impeller that's clogged. Hair & Debris can keep it from spinning, and then you won't have the suction to stick to the walls, or it'll stop all together. I have a dolphin s300, and my impeller motor was seized up. If you can't spin your impeller by hand, it's all clear in there, you have the same problem.
I ended up needing a $450 Motor Assembly, sometimes called a motor controller. The only bad part was the impeller motor inside. I ended up opening the impeller motor, which was pretty easy, and replacing the bad internal ball bearing. Was able to buy that on amazon cheap! Here's how I fixed it! https://www.youtube.com/watch?v=gY3ylcD4JFg
Good Luck!

There are several problems that could make these automatic pool cleaners fail to climb the walls. The cleaner could be too heavy. Empty and wash the filter bag and add floats if necessary. Make sure there is no water in the handle and that the brushes arent worn. If the cleaner is too light, add weights. If there are excessive amounts of algae on the wall, you will need to brush the walls first. The algae can prevent the cleaner from climbing. Make sure that the temp is at least 65 degrees in the pool. Make sure there is nothing caught in the impeller.