Computer Running Slow - Not Just Internet Slow But Onboard Slow

Lately my computer has been extremely slow, not just internet slow but onboard slow. For example, if I click on an application from the desktop it will sit there for 10-20 seconds before anything happens. Occasionally I'll click multiple times on something and nothing will happen then 30 seconds later it will open multiple instances of things. This delay has been happening with just about anything I click on, acting like the computer's busy doing something else when nothing else should be going on. I've looked in the task manager and the applications column will be blank