In some cases of computer addiction, one becomes so dependent on the computer that he or she is depressed or irritable without it. In other instances, a depressed individual uses a computer as a means of escaping one's problems.
Either way, one's mood may deteriote in the absence of one's computer and, left untreated, this may cause one to lose many hours to computer over-use. The resources page provides links to more information and treatment options.