When open ubuntu on virtual box , it doesn't work , and the following message appear "No bootable medium found system halted"
How i can solve this problm?
This error is thrown by what you might call the "BIOS" of VirtualBox. There should be a button you can press during startup to select a boot device. If this doesn't work, you might want to try reinstalling.
If grub2 (the bootloader) isn't installed, the system cannot boot. To fix this, you will need to boot from a live cd, that is, booting from the installation disc and selecting "try ubuntu". Then open a terminal window (search for "terminal") and issue this command:
This will open a sort of wizard with several options. You can leave the text fields at the default value, but make sure to select the correct drive when you are asked. You will need to select the primary virtual hard drive, which most likely would be /dev/sda (not sda1). Look at the size of the drive to make sure that it matches.
After doing this, grub2 will be installed. Please note that this requires a working installation of ubuntu, so if it fails, try reinstalling. Also, there might be several boot options in a menu during boot (the grub2 menu), in which case you will need to find the right one. Once you have booted the virtual machine from the hard disk, you can eject the CD and run the above command again. I'm not completely sure about this last step, and it might not be necessary. Make sure to remove the CD before trying to boot the new installation.