Lcd Screen turns white

Iam a computer servicer with the following problem.I have a Hewlett Packard Notebook computer model Pavillion N5420 in shop with the following problem.
Power the system on & open the lcd screen to view it & at approx 2 – 6 inchs open normal screen can be seen,open screen to normal viewing and screen turns bright white.Unable to seen any thing on screen until you almost close it.adjusting brightness & contrast controls have no effect.I suspect cabling from lcd screen to computer is bad. Hp tech support was no help.Please help me.