Have you heard of these things called sentences? You don't need to hit return between each one.
"Hi Dude, I've got this thing I need help with. Here is the description of what it is and what I am having a problem with."
It's not an issue if they put it in the same chat message, it's the "Hi", send message, "I have a problem", send message, "This is what the problem is", send message that drives me up a wall.
And if you REALLY need him to get back to let you know if he can help out immediately, you can send a second message along the lines of, "And sorry to be a bother, but I need help pronto. Please let me know if you can take a look at this right now." At that point, it's not a big deal if there's another message, because you haven't wasted time in relaying it.
This is what I'm guarding against. I haven't been a programmer long, but it seems inhuman to not try and be polite or have a tiny lead up to the question.
Ironically, it's the exact same thing that makes me impolite.
First of all, you're not bursting into someone's office. Second of all, if you burst into my office while I'm working and start making smalltalk, I will, depending on my mood and whether or not I've previously judged you to be a useless person, either immediately ask you to get to the point, or throw you out.
Stop wasting my time. If sending "Hi" makes you feel better, fine, but the substance had better be on my screen by the time I look at the window, or you've wasted my time.
The same way you know he's not at his desk when you type that useless "Hi": you don't get a reply. How long do you wait after typing a useless "Hi"? Wait that same amount of time after typing your relevant question.