Can you give more information, such as what was wrong with it in the first place, whether you've modified the software in any way (rooting for example)?
All a factory reset does is erase user-installed software and data. It does not alter the system software in any way. So if the display is not functioning now that implies that the system software had been damaged in some way before the reset, and it's hard to work out what just from the information you've given. If you can still get into the bootloader then that would tell you that the display hardware is not damaged.
I'd be tempted at this point to try to reflash the phone software completely - a reset will have turned USB debugging off, and your screen is black so there's no way of turning it back on, which means that the only way of interacting with the phone is via the display, which is blank. However, procedures, tools and downloads needed for this depend on what phone model you have and often what carrier you bought it from.
