I installed Debian 8 on my laptop, all went well. I switched the laptop off and back on a few times over a number of days and it booted into the OS fine.
I have since removed the hard drive and used my Windows hard drive for a while.
I have today put the Debian hard drive back in and it will only boot to the GRUB command line and not the OS.
Why? How do I make it boot into the OS?