The white screen is a sign of a bad connection, or failing screen. Video signal is not reaching it's destination.
If moving the screen sometimes corrects the problem, my first guess would be a poor connection at either end of the video cable, or bad video cable (usually around the hinge).
If your doing the work yourself, always make sure it's unplugged, battery removed, and power is drained (hold down power button). Unplug connections and make sure they are plugged back in and well seated.
I'm pretty sure that the screen in the G550 has an LED backlight. Inverters are only used with the older CCFL backlights. Besides, if it were, and the screen remains illuminated - the inverter would be working.