I think "不好“ better translates as "not good"
for the meaning "no good" (which has a sense of personal assessment as poor quality) I'd use cha4jin4r (差劲儿) or cha4jin4 差劲
Ex.
你不行！You don't get (how to do) it!
我们本来觉得你能来，但是后来你不行。We thought you could make it at first, but it turns out you can't.
你不好！You're bad (at it)!
你干什么？你这样不好！What are you doing? That's not how to do it!
你很差劲！You're really no good!
我电脑不行。My computer [isn't working/doesn't work].
是苹果软件，我电脑不行。It's an apple program, my computer can't run it.
我电脑不好。My computer isn't good.
我电脑差劲。My computer's no good.
Also note, for children's or pets' "good (behavior)," don't use 好, use guai1 乖.
你好乖哦。You're so well-behaved.
你周末怎么从来不出去？多么乖的孩子！How come you never go out on weekends? You're such a good little [boy/girl]!
不乖。Bad [boy/girl].