Well, your room mate may be a fat clumsy nerd (or he may not be) but he is perfectly entitled not to let you use his computer. Most people store private stuff on their computers, and if you behave in the way you do, I'm not in the least surprised that he wants to keep you out of his private life as you're obviously not to be trusted.
If he genuinely suffers from a mental disability, shame on you for behaving like a big bully . If I'd reacted like you did and attacked him, I'd be too ashamed to boast about it on a website.
If you had any decency, you'd go and apologise to him and in future not put him under pressure by asking to borrow his computer. Save up and buy your own.
And you're studying physics? Heaven help the future of the planet if we have to rely on specimans like you to save us ! We seem to be witnessing the fruits of Tony Blair's Education policy.