A little clarification will help here. I would like to know as to when you receive the black screen. Is it at the initial startup or after you seeing the Windows Logo. Or you see a blinking cursor to the top left of the screen?
This symptom (blank screen with cursor at the top left side of the screen) in most of the cases indicates Hard Drive issues. I can try assisting you with troubleshooting. Please try the below mentioned steps and check if this helps:
1. Check in the BIOS if the Hard Drive is detected.
2. If the Hard Drive is not listed in BIOS, Load the BIOS Defaults and then restart the computer.
3. If you again get the same screen, take a technician's help to reseat the Hard Drive (if you wish to do it yourself you can refer to the service manual).
4. After reseating if the Hard Drive is not detected again, you need to replace the Hard Drive.
5. If the Hard Drive is listed in Step 2, run the Diagnostics provided by the manufacturer (if any) on the Hard Drive.
So that I can provide you the details on how to perform these steps, in your reply please include the System Model Number of your Gateway Computer.