Try an SMC reset.
After powering on the laptop wait a few minutes, then press the Caps Lock key to see if its LED lights up. If it lights up, then most likely your laptop is booting, but has a defective built-in Display. You can try using an external display to confirm the issue although you may need to put the laptop into Clamshell mode by closing the display so it forces the video to the external display.
If the battery was completely drained, then let the laptop charge for a day or two to see if the battery will begin to take a charge again. If the battery was discharged for any length of time, then it may prevent the battery from charging again and even prevent the laptop from powering on. Sometimes it is possible to disconnect the battery and power on the laptop using only the charger. If the laptop powers on with the battery disconnected, then re-connect the battery while the laptop is still running and plugged into the charger and allow the battery to charge at least 10% before turning off the laptop or disconnecting the charger, otherwise permanent damage to the battery may occur. You must be very careful not to have the internal circuitry come into any metallic or conductive surface/object.