I installed Ubuntu yesterday but it does not work when I try to access it. Instead it sends me to GRUB 1.99 . What can I do to make it work normally? What are the commands that I have to give for it to function normally?
Reinstalling the GRUB2 boot loader to the Master Boot Record often solves this sort of problem (assuming you're describing a grub> prompt with a flashing text cursor instead of a menu where you can select what OS you want to boot). You can reinstall GRUB2 to the MBR using any of the methods detailed at https://help.ubuntu.com/community/Grub2#Reinstalling_GRUB2.