I wonder how much those interpretations can be altered, though, playing around with the context in a way that would make them more fully generalizable. For instance, if the with topic modifier pronoun この is dropped and a topic marker for the speaker added...
コンピューターは使えません
Given the implied context of 私は, for instance, this is very commonly translated into English as "I cannot use computers." Whether other people can or not is not the concern of the speaker so it is left unstated. The emphasis and implication with は is that there is something else that can be used. Is that a misleading or possibly very natural way of thinking of it?
Again, without the この indicating any computer in particular, are が、を not also being used to convey the message that the speaker is unable to use computers in general ? Whether anything else can be is ambiguous.