Yes, if it is part of a leading dependent clause, but it technically requires an understood word or two.
Example:
"Unable to change its course in time, the ship collided with the bridge."
"Unable to recover his lost calculator, Bob was forced to buy a replacement."
I was unable to go to the carnival because I had loads of homework.
I am unable to read your scrawl.
It's so frustrating that I can't fix it myself, but I am unable to lift it.
'The beneficiary is unable to speak due to her disabilities' is correct.
No, you cannot start a sentence with "no" unless you need to do so. No reason exists not to start a sentence with that word, as you can see. No one will care if you do start a sentence with it.
Yes, I can start a sentence with "Is."
"we were unable to get expiation from the local store"
I am unable to describe his unique mode of dress.
We were unable to squeeze an executive briefcase in.
I have no wings, hence I am unable to fly.
It is not acceptable to be unable to use acceptable in a sentence.
Yes, you can start a sentence with a verb.