Over time the hard drives wear out causing the start up and even use to be very slow. Usually it's a sign that your hard drive is on its way out. On your model the specs indicate you have a 500 GB 5400 rpm SATA. You can resolve this buy cloning over your data or backing up your data and either replacing the hard drive with another hard drive or I recommend installing an internal ssd. I've done this on many older laptops it bring them back to life and makes them faster.