I don't think you should require a paging file so high normally, so its possible that you may have a DOS (Denial of Service) virus or something which is using up a great deal of your RAM, but you probably would have noticed the CPU usage if there was. With regards to the paging file, the way it works is that it uses ROM as RAM, so technically you should be able to set it as high as you want, but regardless Windows only lets you use around 4-6gb max, I think