In a network computer system, recovery may be impossible from a fault when the fault occurs in a network switch in a network or a device such as an external disk device. Provided is a computer system that includes a plurality of servers, a plurality of network, a plurality of external disk devices, and a management computer, in which the management computer detects a fault which is occurred, retrieves an application stop server inaccessible to the used disk due to the fault, retrieves the disk for storing the same contents as contents stored in the disk used by the retrieved application stop server and the external disk device including the disk, retrieves an application resuming server capable of accessing the retrieved external disk device, and transmits an instruction to boot by using the retrieved disk to the retrieved application resuming server.