There are several reasons why you have a black screen.
1. One of the causes of this type error may be a faulty video card or display adapter. The obvious sign of a faulty video card is lines flashing or appearing continuously, yet no display at all.
2. Another cause of this error is when the RAM is faulty, not firmly fixed, or if it is absent. Some computers normally beep when RAM is not installed, while others do not make any noise, but only show a black screen.
3. Black screen error may also appear when a new hardware is installed into the computer motherboard. This is mainly due to the incompatibility of some hardware with the computer system, particularly the motherboard. The best solution is to remove the hardware, then restarting the computer. For other options check here What should I do when my computer starts with a black screen? | Techyv.com.