Have you been able to come up with ways to wear his butt out! Riding bicycles (mine had a motor so i could hope to keep up!) or jogging or trampolining or swimming in lake, treadmill, special tv show that goes on walking the treadmill, anything to drain some of this energy. Anything physical he already likes. Never ever alone, obviously, so me too, just me, no friends family or heartwarming magical town of supportive whatnot, that's life. Also no friends family making more pressure, so, not complaining.
I don't know what you mean by severe autism, for my mind this means almost no ability to communicate to him or him to communicate to others. So let's think about the adhd...especially the H in adHd.
By severe adhd, i'm thinking the type that seeks more and more stimulation, more action or toys or tv's - no a bigger one - no this one - no the giant home theater!!! I need a model plane, now it's boring i need a jet, did you see the rocket i need a rocket!!! Not like a shopohalic...don't mean that. Just a mind that devours continual stimulation, seeks it with impulsive high interest. HIGH interest is the only interest. A constant seeking of the next high to the exhaustion of those around him. Is it like that?
Autism, always struggle to shift focus/priority. To think 'eh, good enough'. Non autistic struggle too, but not always unlike asd. Add to that, marking memories when the 'fail' happens....ice cream falls off cone, 'whole day is ruined' and forever the memory is of the 'fail'. Yes, non autistic do this too, but can recover, get another, move on, or at least not wind up so you never go near the ice cream store again and take different streets home years later it's a meltdown again. Is this struggle to shift focus and move on, your son?
So X gets a picture of what he will have, goes to you given you are the only path to get this need met, if you say no in any way including that the item is not yet available for purchase, bang, now you are the OBSTACLE. Not sure how this became violent, likely gradual, you both ran out of options so his is hit and yours is get hit currently. You said it got worse a few years ago, puberty can fuel everything you're saying.
He has energy, and no other source to get 'need' met. By default, you are the obstacle, he's practical, does not destroy objects that meet needs, so has regulation of actions even without regulation of emotion...this is very, very good. Kudos to him. Something to recognize, build on.
If he is violent restrain him yes, yes, yes, assuming there is no way to ask him while calm what he would like to keep you safe. If he slices his finger punching your mouth, the ER sees your fat lip and his hand...enter social services. ya see? Feels like violation to restrain i know. I asked my son what to do, after first restraining him i felt so sick, i knew it overwhelmed him.
He was 10-11 or so, near tall as me, he asked me to put him between the mattresses and 'squeeze' him....HE thought of this, not me. I thought he was brilliant, was told never to do this by everyone. Seriously? His body, not head! First try i ask him "squish more, you ok?" dunno what to do. He is my guide....'more, more, more....ok stop stop...more, more'. When his sensory (tactile?) need was met, no violence. NO IDEA if the same is true for your son...but...hope you know it's beyond spoiled, brat, just say no, etc.. and not due to 'bad' boy.
I just keep wondering, seems a pretty reasonable mind that does not destroy everything in a blind fury. That is reasoning, rational, to me anyhow. Seems he has things to work with, qualities to praise (unless you think by praising him, he will think ah ha, i see, destroy the computer) and you're for some time now being put in a position to work against the behavior without explanation of what he is thinking. Then, put in a position of being a frustration to him.
When adhd bodies move move move, their brains calm. If the body doesn't move the brain moves double time. Son needs to bump and body slam off the hallway walls, where as the girls just walk down the middle. Adhd needs tactile feedback feedback feedback...stomping, jumping, crashing...no gentle anything. So without getting all psychology-blah-blah-blah it'd sure be nice to get an explanation of what he GETS from a sensory standpoint, physical aggression is tactile, it is touch, albeit not soft touch.
Try to find cause/effect thoughts with absolutely no good or bad attached. My heartfelt motherly prayers he is able to know and convey what he needs, to avoid getting aggressive. Most ofthen not that simple, once in a while it is. You cannot hit, what do YOU like, what do YOU want...spraying with hose, twirling yourself on chair, song over and over, making a (child's name) mattress sandwich, etc... give him a menu of choices to choose from.
Look up ideas to tucker out kids or teens with adhd. One day my son found a penny, then melted down when another was not found in a few minutes. I had to hide a penny every so often in the grocery aisle...where he could see it. Just keeping him near is hard enough. turned into, he and his little sister being so interested in finding a penny (each!) I could shop. They stayed in the aisle with me! Had to first, let them ahead of me in aisle to plant a few pennies. Our new 'rule' is mom goes down aisle two times. Second pass, they find pennies. Of course I'm feverishly watching them, any cart coming down aisle from other shopper, learn a rhythm that works eventually. No real reward!!! They'd just bring them back. I'd plant pennies in next aisle while watching them search, second pass down aisle they would find. Repeat. No idea why it worked, it evolved when i see HIS interest. In time, he can get enough for a nickel and so gum, which, never do i buy, now he has this power...can find pennies to get gum mom says no to. Kind of funny, he'd say, "sorry mom" and shake his head chewing the gum, just like i shake my head saying no. I'd have him and his sister jump from square to square, they were maybe a few feet apart, that ugly linoleum design...gave him focus, that idea i did apply from an adhd pamplet long ago. Would it work, is it possible, if you hid five bucks in change per day into the lawn, that he would be so in the 'zone' picking them up focused on what he could buy with enough...yes i see all the pitfalls of that. Point being, worth a few bucks a day if it keeps him enjoying a quest for coin, busy for hours, and allows him to make choices to buy...don't need to grasp money, put dots on a paper, when quarters are on all dots you have $20 or what ever amount. Maybe unrelated to computer advertising stuff, separated worlds. ONLY HE can get these things from his quest and treasure finding of coin, he's PROUD, mom can't, too bad...make a menu of what he can get. Sometimes, who cares what causes behavior or why, tell me what to doooooo!
Really tried to make up for previous potty training post. Hope anything helps. ALL MY BEST.