If you're pushing the "On" button and nothing is happening , then there is a slight chance that the switch is bad ! Usually when they won't turn on , it's the motherboard is going or is gone ! Check all your connections and make sure it's getting power ! I would have a Tech check it out to make sure ! If it's an older computer , then it's probably the motherboard ! Have someone check it out before you start spending money on it ! How old is it ?
If you don't know how to turn it on, return it. Did you plug the power cord into the little square box on the wall in case the battery needs a charge? Do people seriously ask these questions? Apparently so.
Press the power button on both the CPU tower AND the monitor. If that doesn't work, try plugging in what isn't plugged in. Mouse=USB outlet on back of CPU Keyboard=USB outlet on back of CPU Main power cord=connects from an outlet from CPU to wall outlet One of the cords on the monitor=wall outlet Other cord on monitor=CPU outlet.