IN my company . . . .some 2 Systems are having problem wat probs i m not g

Hi guys . . my system is not at all starting . . no beep sound . i checked hard disk . . ram and bus . . .from smps power also coming . . .i removed every dust. . .i cleaned properly . . i connected everything once again . . then also its not working . . .wat may be problem . . .plz help me