Which noun should I use to describe that a computer system hangs?

According to the dictionary, "hang" can also be used as a noun, but I don't think it is the right word to use in this scenario. Should I use "hanging" instead, e.g., this software bug may cause two problems to this computer, crash or hanging? It also sounds weird to me.

In general, if a verb doesn't have a direct corresponding noun, what should I do if I have to use a noun to present the same meaning.

You could say "a freeze", but "a hang" is also perfectly acceptable.

As a matter of fact the title of the wikipedia article "Freeze_(Computing)" is actually... "Hang" and starts like this

"In computing, a hang or freeze occurs when either a single computer program or the whole system ceases to respond to inputs."

(emphasis is mine)

Personally I would prefer to use a "hang" for a server (typically in the case when a request is sent and one waits indefinitely for the answer) whereas the "freeze" conjures up the idea of an unresponsive GUI (when for instance moving the mouse does not move the pointer) and would therefore preferably apply to a desktop.

In at least some technical communities, a hang is perfectly standard, and probably the correct term to use. Try googling, for example, "fixing a hang" or "server hang":

We will go over the basic debugging of a server hang in a future post.

If you don’t like that noun usage, then reworking it to use a verb is probably the best option, if there’s a reasonably non-clunky way to do so.

I’d be rather wary of substituting other nouns (freezes, crashes, etc.), depending of course on context. As with all technical and semi-technical terms, there may be subtle distinctions between their precise meanings, which it’s important to respect. I don’t know what the usage is now, but at least on Macs in the early 90’s, if I remember right, a freeze and a hang were two specific types of crash — to a lay reader they sounded like synonyms, but when the technical details mattered, they weren’t quite interchangeable.