|Dell "flat screen monitor" doesn't tell us whether it's an LCD or a CRT monitor - both can have flat screens. . |
If it's an LED monitor, and it it does the same thing when you connect it to any computer, or if it's the LCD display built into a laptop, it can be fixed, but if it's the backlight that's dying, that's a finicky job - most people just get another standalone monitor, or get a new or refurbished (if the backlight was actually replaced by a pro) display assembly for a laptop.
For some info about replacing a voltage inverter or backlight, and what some typical symptoms are, see response 5 in this: