Expert system is an application of artificial intelligence that gathers the expertise of the experts and makes it available for the non-expert user. In this paper, an expert system is designed to diagnose the network connection problems in the computer. The database is built with Prolog and Java is used to build the user interface, and JIProlog is used to connect them both. A case study performed in AlNahrain University campus to test the system performance and the efficiency of the user interface. The results show an efficiency of 82.5% and ease of the Java interface for the users. The non-compatible operating system, Java failure, and the language difficulties for the users were behind the 17.5% efficiency failure.