Black sreem on a compaq labtop cq50-215NR compaq

1 disconnect the AC adapter and remove the battery from the laptop
2. Press and hold the power button for 30 seconds
3. replace the battery and connect the ac adapter to the laptop
4. turn On the notebook and check.

If the issue persists, restart the notebook and press F10 to check if you see the BIOS screen. If you cannot see the BIOS screen then the issue could be hardware issue and your laptop needs to be repaired