Best thing to do would be to check your
CPU performance in Task Manager.
To do this either right click on your task bar and select task manager or press CTRL ALT DEL and choose Task Manager.
Once in there click performance and see if how much usage your
RAM and Processor are getting.
Also check under processes, you should be able to see which program is using the most memory and
cpu e.t.c and then depending on the program you can choose to "end process"
Also how long has this been happening because if it is only quite a recent thing then you should check to see what new things you have installed (be it hardware or software) since then.