You may need to upgrade the memory in your computer. To check this, right-click on the clock on the bottom right of your screen. Left click on Task Manager, click on the Performance Tab. (you may have to expand the selection). Note the amount of memory in use, the amount of memory installed and the percentage of memory used.
As Operating Systems get larger, sometimes it will outgrow the amount of installed memory forcing the computer to start swapping a lot of memory to the hard drive. If your system has only 4 gb of memory installed then you need to go to the manufacturer website or crucial.com and purchase a memory upgrade. Most modern systems need a minimum of 8gb of DRAMM memory and 16gb is preferable.