My computer has been running really slow

Greetings everyone…
Please help me with my problem. My computer has been running really slow and I don’t know what could be causing it. When I checked the Task Manager, it indicated that my CPU usage is 100% but when I looked at the Processes, the CPU usage drops to 0 and then shoots up again to 99%.
I think this is what’s causing my computer problem and I really need to know how I can solve it.
I hope you can help me.
Thank you.
