Aloha K,
Sounds to me like the disc is bad/scratched etc.
1-Will it even ‘mount’ in the Finder?
2-Even before trying to install Cubase. can you ‘see’ it
on the desktop or in the Sidebar?
3-Is there another 'puter availble to try?
If the answer is no to either of the above and since you ‘bought’ it,
send/take it back and ask for a replacement disc.
{‘-’}