Camera is on but not lcd picture why

Hi @banamalimohanty ,

Try taking some pictures (I realize that you cannot see what you're taking) and then download them to a computer and check if they're OK or if they are just black images.

If the pictures are OK then it is either a failed screen backlight (faulty backlight power supply from motherboard, a loose backlight power cable connection from the screen to the motherboard (see smaller flex cable in this image of the LCD screen (supplier example only) or most likely a faulty screen.

If the pictures are just black images, then it could be a faulty motherboard. If it were only a faulty cmos sensor in the lens then you would still be able to view the camera settings menus on the screen.

If it is determined that the problem is the LCD screen here's the ifixit Nikon Coolpix A900 Monitor Replacement guide that may help. Search online for Nikon Coolpix A900 LCD screen to find suppliers that suit you best.