So Australian consumer Law is one of the strongest in the world, it requires goods to be warranted for "a reasonable lifespan" which is independent of the manufacturers warranty, from what it says in the article is say that umart are calling foul of multiple posts of Australian consumer Law, reasonable lifespan and right to choice of repair, replacement or refund.

As to their statement of it being a minor fault I would say in response that it causes the PC to be unstable which would be a major fault in my books.

Here is the link for the ACCC page, it you're Australian I strongly recommend you check it out.