Dell N5010 sometimes screen works sometimes gives 8 beeps

I have a Dell N5010 with amd 5650 graphics card.

My screen is causing problems. System gives 8 beeps on start up but once I connect it to an external monitor, system boots without any beep. And after a few boots with the external monitor attached, the laptop screen also starts working until it decides to stop working again :\

The laptop screen shows small squares and bars of different colors. These are also visible on the external monitor.

I guess there is a bug in video driver or BIOS. I updated video drivers from dell yesterday but the problem still persists.

Here is the Windows error report after it shuts down abruptly:

=======================================================

Problem signature:
  Problem Event Name:    BlueScreen
  OS Version:    6.1.7601.2.1.0.256.48
  Locale ID:    1033

Additional information about the problem:
  BCCode:    116
  BCP1:    FFFFFA80068204E0
  BCP2:    FFFFF88004006C48
  BCP3:    0000000000000000
  BCP4:    0000000000000002
  OS Version:    6_1_7601
  Service Pack:    1_0
  Product:    256_1

=============================================

Can someone tell me what shall I do to fix this problem .