Help installing Ubuntu Mate

[Linux for blind general discussion]

I didn't have good luck with Vinux so decided to go with something
more mainstream. I have a bootable DVD and I managed to boot from it.
I heard the drum sound which indicates Ubuntu has started. BRLTTY also
started and gave me its useless 'screen not in text mode' message. But
Orca didn't speak when I pressed alt-windows-S. Why, and what might I
try next? The goal is to install to one of my hard drives. Thanks.

Amanda