Hi,

Sounds like a backlight problem. I had a Proview BM568 in for repair
with the same symptoms, and it turned out to be the SMD fuse on the
inverter board open-circuit.

Be very careful with the inverter board, the little transformers on it
deliver very high voltage to the CCFL (Cold-Cathode Fluorescent Lamps)
tubes and there will be high potential even on the transformers' cores,
so you don't want to be touching any part of them or the circuitry
taking the voltage from them to the lamp connectors.

You can sometimes tell if it's just the backlight not working by
looking at the screen carefully whilst a video input is connected and
using a torch angled towards the screen to get some reflection from
behind the LCD display. If you can see some of your desktop (if using
Windows, say) then the screen is functioning but the backlight isn't.

If you need more fino or help, just say so and I'll be glad to advise.

Best regards,
James