Could be a lot of things. First question I have is what F8 has to do with startup? Things I would try:
Try to hold the power button down for about 10 seconds, wait a few seconds and then power up. On most machines, that will do a hardware reset.
Is there a disk activity light (usually there is) and does that flash for several seconds when you turn the machine on?
You can check the display by shining a light on it and seeing if there are faint images (that would reveal a broken backlight).
If you have an external display, plug that in. You may have to hit the display select key (fn F3) on my machine but different on other machines. I would hit that key twice and then hit enter to select the external display.