Connect the power cable AC adapter, if your laptop is running on battery power only, connecting the AC adapter may solve the problem. Ensure the adapter cord is correctly plugged in on both ends securely. If the laptop works with the adapter plugged in, your battery is dead or defective.
Remove and reconnect the battery, many new laptops (especially MacBooks) are using the new design that does not allow their batteries to be removed. If your laptop does not have a removable battery, skip to the next section.
The laptop can also be in a power state that prevents it from booting. Disconnect the power cable and then remove the battery from the laptop. Leave both disconnected from the laptop for at least a minute. Then, put the battery back in the laptop, connect the power cable, and try turning on the laptop.