Toshiba Satellite c55 c55d laptop display not working. Does work with external monitor via HDMI. Screen replaced, backlight comes on but no display. Have tried taking out the ram putting it back in (haven't replaced it with new ram yet). Have tried taking battery out and restarting with shift + f8. Tried toggling screen. Any suggestions?
Well, if the external monitor works fine it isn't your graphics card/GPU, so that is wonderful.
You said you replaced the display. Did you make sure all the connections were good and solid? Also did you perchance reuse the same ribbon cable? If so, you first you might want to disconnect it and do an inspect of the cable. Make sure you don't see any damage, even small damage, on it. And make sure it connected securely.
If none of that helps, you may want to try replacing the cable.