ctrl+alt+delete+ "sart task manager"and have a look at processes and see which one is using all the cpu and to determin if its needed or not, if its not then you can stop the process and see if the cpu usage falls!
virus/spam etcetera got installed on your pc some how.even if you end process in task manager most just start right back up.i suggest you use malwarebytes here- http://www.malwarebytes.org/mbam.php