First check out if it's an inverter/backlight problem or it's a group of pixels behaving badly.
Look at the display (put on a white or lightgray screen) from a very short distance. When you definitely see some groups of pixels flickering (and others remain stable), this means the pixels are blinking. This could be caused by the display itself, or the video card. When an external DVI monitor has the same problem, it's definitely the video card (unlikely though, because the video card has 2 separate video outputs).
An old cracked or scratched TFT panel can come in handy to use as a test display (also to test the backlight).
When it's more like a horizontal region on the screen that is flickering, the problem comes from the inverter or one of the four horizontal tube lights. The inverter has four output stages, each driving a lamp. Exchange 2 lamp connectors to see if the flickering region moves. When it does : exchange inverter (or try to repair it : maybe the cores of the step-up transformers (ferrite) are loose and have to be hot-glued).
Flickering remains in the same area : tube light in TFT panel defective. These are very hard to replace (I never had to try this), and they don't sell it in the lightbulb store.
To be sure you need a (borrowed ?) test display before buying a new one.
When the whole screen is flickering : check wiring to inverter and inverter itself.
Good Luck !