Dell U2711 startup issue

Hi,

I have a U2711 monitor and I really happy with it ... but last night when I shut down my computer, in the left of the screen is black and the right side is dark blue in the black background, I don't know what it is and I try to find out. But it only happen when the the computer is shutting down and has no signal at all. I try to un-plug all the signal cable and try to turn on and off the monitor, but sometime it work fine, sometime it appear this problem again in the black background (about 30%), I guess it could be either the monitor or cable only. Any advice would be greatly appreciated.
My monitor has the same problem with this monitor. http://en.community.dell.com/support-forums/peripherals/f/3529/t/19435076.aspx . Can anyone explain for me what happen and how can I fix it because the warranty of my monitor is expired.

Thanks

bungativn

p/s: sorry because my bad English grammar, I'm not a native speaker.