When you experience high memory usage on Windows, but when you open Task Manager, you don’t see any program using too much memory. There is some memory usage that is not visible in task manager, i installed RamMap , a part of SysInternals tool, i was able to find the hidden memory usage. I can quickly free that memory by going to the menu Empty -> Empty System Working Set.
Thanks to this Post
https://channel9.msdn.com/Events/TechEd/NorthAmerica/2011/WCL405