Presario s4020wm tower

Start with the power supply and verify that it working if not replace the power supply with one that is known to be good then if you still have no power check to see if the voltage selector is set to 115 not 220 if this all checks out good than you will need to verify that all the connectors to the motherboard and all drives are secure i have got a lot of dead computers to come alive just by unhooking the power cord to the computer and opering up the tower and 1 by 1 unplugging and replugging in all the wires to the board and harddrive and cd rom and dont forget about the cmos battery and than pressing the power button for 3 seconds than plug in the power cord to the computer and try to restart ok good luck !!!!