What should I do if the computer doesn't power on?

First, connect the AC power cord securely to an electrical outlet and verify all ATX power connectors (ATX_PWR1 and CPU_PWR1) are properly connected from the power supply to the motherboard. Check that the power supply unit has its power button turned on if it has one, ensure the power switch cable is connected to JFP1 properly, and verify the Clear CMOS jumper JBAT1 is set to Keep DATA. If the issue persists, test with another known working power supply of equal or greater wattage.