Depending on your VM (particularly hyper-v) you may have a problem where the disk is not correctly picked up after your first install. If that happens, before you reboot for the first time you need to edit the file /boot/grub/menu.lst
In there you will see references to /dev/disk/by-id/xxxxxxx – remove those and replace them with /dev/sda1
That will resolve your boot up problems. Here is a video available as well.