How much memory have you got and what is your operating system? The cause of this problem is that you have to many programs loaded up and not enough memory.
also boot from a usb stick and run hard drive vendor health tool and hd tune read the hard drive smart info. see if the drive is healthy. if it is try booting in safe mode run malware and anti virus scan. also run ccleaner. check that there some empty space on your hard drive for the computer to make a swap file.