First, inspect the cable for the LCD to make sure it did not tear when pulling through the frame. Next, inspect the connector on the board and the part to ensure there is no plastic or other debris in the way of a solid connection.

You may also want to try and reset the device by holding the sleep/wake and home button at the same time until it turns on with an apple logo (or the backlight you mentioned).

I had the same problem. This is how I fixed it.

Remove the LCD cables, Place some windex on a napkin, wipe the connectors. There might be some windex left on the connectors, so get a dry napkin and dry off. Make sure you put back the conncetors correctly and it should work. It did for me. I only removed the battery to avoid a short circuit. and the plate that covers the LCD connector so you dont have to tear the whole thing apart. GOOD LUCK. Hope this helps some of you.

I recommend connecting your old screen back on your phone. If old works, then new one is faulty and needs to be returned to vendor.

RESET THE PHONE!!!

I had the same problem... Reset and now its all back to normal... Thanks Garry!!!

This is the problem for the display connecter.

Resetting the phone is your best bet. You can do this by holding down the sleep/wake button and the home button at the same time for about 5-7 seconds.

You can also simply disconnect and then reconnect the battery. We have to do this quite a lot when testing LCDs internally.

Hey everyone i had the same problem, the lcd is damaged bottom line. I had 2 lcd replacement one was the lcd with the digitizer and the other one was just the lcd both new. the one with the digitizer & lcd gave me the black screen, when I tried the solo lcd it worked as it should. So just get a refund or exchange

Yes I had this too, you need to replace the backlight IC.

If you guys replace it with the iPhone 4 LCD Touch Screen Digitizer that is pre-assembled, it will never occur the problem

So after trying the 2 LCD's that didnt work. I decided to cut my losses and just throw the old broken LCD back in and sell it on eBay as a broken device for parts and just report the problems that it was having. To my amazement it fired right up with no display problems at all. I guess it was just an extremely unlikely coincidence that I had two screens that were duds in a row, (I've done 40+ screen replacements and these were the only duds I've ever encountered.)

I know that I'm not the first person to mention this in this thread, but if you are having this problem I would highly suggest trying the original LCD back in it just to see if you have a bad screen.

The same as a poster above, I had the same problem. This is how I fixed it.

With the back of the phone open, disconnect the battery (step 5), remove the wifi antenna (step 13 and 14) and then disconnect the LCD and digitizer cables (step 17). I sprayed some windex onto a clean, thin cotton rag, like the kind you can buy in boxes at Home Depot, and gently wiped both sides of the LCD and digitizer connectors. I then reattached LCD and digitizer cables and battery and back case, and the screen fired up. This worked after multiple attempts at reassembly without using the windex, so the light application of windex seemed to be the trick.

Two other things, on this reassembly, I had a lot of difficulty getting the LCD connector to snap into place, I suspect that on earlier attempts I may not have had the connector aligned and connected correctly.

Second, on this reassembly, I was in a rush and only tightened the wifi antenna enough to hold it in place, I did not crank down on the screws that hold the wifi antenna. This might have also affected the LCD connection, if I had been overtightening before.

GOOD LUCK. Hope this helps some of you.

It could be this:

http://www.youtube.com/watch?v=lnkSMtUV8...

Just RESET the phone (press and hold the home and power buttons for about 10 seconds and then let them go. Then press and hold the power button for about 2 seconds to turn it on)... As I said earlier.