Chosen Solution

i have tried few ideas :

  1. remove battery & power plug then push power button for 1 min.
  2. remove ram and insert it again
  3. press D+Power button
  4. fn+ Power button. but none of this work… have you any idea accept this…?? what is the reason for this 8 beep & black screen?? Update i tried that option with HDMI cable Fn+F1 keys to us the external monitor. .. but it still beeps 8 time… and i think its not detecting HDMI… what should i do..?

The 8 beeps that you are receiving from the computer would indicate an issue with the LCD screen. I would suggest you to connect an external monitor with the system and press the Fn+F1 keys to us the external monitor. If the external monitor works then i would recommend running the LCD Built-in Diagnostics which the instructions can be found here - http://www.dell.com/support/article/us/e…

what i found was when dissassemble screen that the cable somehow came loose. just plug back in correctly.( use scotchtape or other ) to hold secure.. problem solved