A grub prompt is most likely coming off the hard disk where you're attempting to boot.
Restart the machine and adjust the bios settings so that the PC will attempt to boot from the CD or DVD drive before attempting to use the hard disk.
It's possible that you may need to burn a new image of the sun solaris ISO. That may be where you need to get help, if your system doesn't seem to be able to boot from this CD but CAN boot from others.
Answers & Comments
A grub prompt is most likely coming off the hard disk where you're attempting to boot.
Restart the machine and adjust the bios settings so that the PC will attempt to boot from the CD or DVD drive before attempting to use the hard disk.
It's possible that you may need to burn a new image of the sun solaris ISO. That may be where you need to get help, if your system doesn't seem to be able to boot from this CD but CAN boot from others.