Try Settings, Apps, swipe to All, scroll to that app, select Clear Cache, and follow with a Power Off and Restart. If you prefer, and the options are there, you could select Uninstall or Force Stop instead of Clear Cache.
Get back to us if you still have problems.
Power Clean is one of those apps that, if you find it on your phone, you should uninstall it. It's costing you battery, wasting RAM and not doing much to help you. Android has a much better memory manager than any of these "cleaning" apps. Read Multitasking the Android Way (by one of the people who wrote Android) to find out why.