New lcd screen for p30/35 is showing very dark?

If you wish to get some details; check the site linked here. Pull up older posts.
http://electronicshelponline.blogspot.com/
Faults & possible causes to LCD & Plasma screen are given with illustrations. You can get an idea about the fault to an extent. Faults to all LCD & Plasma screen are similar, irrespective of its brand and screen size.

i guess there is some problem with your panel. make sure you show it to the nearest service centre

Have you tried an external monitor?

Plug in an external monitor and see if the display shows up on it. It can be any kind of monitor even the old big fat crt monitors as long as it has a vga cable to connect to your computer's vga port. If the display shows on the external monitor that proves your video card is ok and your lcd screen is the issue. The video will show on most systems when you reboot without you having to do anything. Some systems will require you to hit the FN (Function key) + F1 thru F12. Hold down the FN key then hit the correct key for displaying on the monitor (F1 thru F12). The correct key will normally have CRT/LCD on it or it will have the icon of a display.

If is shows on the external monitor, then you would have to question if the new screen and lcd inverter is bad. Just because they are new don't mean they work. Are you sure you purchased the lcd screen and inverter that is for your model?

The used inverter maybe faulty. The inverter supplies high voltage to the CCFL lamp in the LCD screen, the CCFL lamp provides the backlight.
LCD screens and Inverters are available from this WEB site.www.lcdparts.net