An apparatus includes a computer chassis and a motherboard. The motherboard defines a rotating hole, a clasp hole, and a through hole. The clasp hole has a clasp slot and an arcuate groove. The computer chassis includes a bottom plate, and a first, second, and third convex projections. A rotating shaft is formed on the first convex projection. A mounting hole is defined in the second convex projection. A clasp is formed on the third convex projection. The clasp includes a root connected with the third convex projection, and a bent portion. The motherboard is rotatable between a first and a second position. In the first position, the rotating shaft of the first convex projection is inserted in the rotating hole, and the bent portion of the clasp extends through the clasp slot. In the second position, the root of the clasp is located in the arcuate groove, and the though hole of the motherboard is aligned with the mounting hole of the second convex projection.