You may have a bad main board or a faulty display adapter.
Some things you can try:
1. Connect an external monitor, if possible. If you get a picture, then the issue is with the internal screen or video cable.
2. Try new RAM, or test the laptop on one stick of existing RAM at a time, if available.
3. Reset BIOS and EC chip by removing the battery and power adapter, then remove the CMOS battery and leave out for 15 - 20 minutes. Put everything back and test again.