Sometime No Display Lcd But The System Is Ok With External Monitor.what Can I Do

 its working fine wid external monitor , so graphic chip should be working fine

check for ur LVDS cable

Connect an external computer monitor to the laptop. If the external monitor display is fine, then you have a problem with the Laptop LCD screen or the LCD cable connection. If the external monitor image is the same as on the Laptop LCD, then it is likely to be a faulty integrated onboard video, this means replacing the motherboard of the Laptop.

A typical Laptop LCD display assembly

The above simplified block diagram illustrates the basic components that are involved on a Laptop LCD video display problem.

Connector Locations 1 - 2 - 3: Video data is sent from the motherboard through to the LCD screen at connector 2. The video cable also feeds voltage to the FL inverter board at connector 3. 

FL inverter PCB Locations 3 -4: This section converts the low voltage DC source (connector 3) to high voltage AC (connector 4), as required to energise the backlight bulb. If the FL inverter PCB is faulty, the LCD screen will appear as a very dim image on the Laptop display screen.

CCFL (backlight bulb): When the backlight bulb is working, you can see the image on the LCD screen. With some Laptops, the backlight bulb is a part of the LCD screen assembly and needs to be replaced with a complete LCD screen assembly. It requires a specialized Laptop repair workshop to replace the backlight bulb.

Laptop Lid close switch: This switch is a small switch (mechanical or magnetic) that is located close to the rear display hinges. Most laptops will either hibernate or operate in standby mode when the LCD is closed. This is achieved by interfacing with the Laptop's BIOS power management software. In turn this is linked to the Windows operating system.

You may opt to have some of the above components checked by a professional.