My ubuntu 16.04 is booting really slowly. I had windows and ubuntu dual booted (ubuntu grub) and everything was just fine. I installed kali (and kept kali grub), and windows and kali booted just fine, but ubuntu turned really slow. I eventually retrieved ubuntu grub using this then entirely uninstalled kali using this (i opted for the virtual machine), but it's still booting really slowly, and windows is still fine. How can I fix this?