Screen is black & unresponsive after opening

1. iTunes does not recognize the phone

2. I tried the home button + power button for 10 seconds but no result

3. I can't see anything when I shine direct light onto the screen

4. I can't tell if it's on or off because it's just black, therefore I just kept trying to hold the power button on and off

5. How much does the repair cost?

6. How much does a diagnosis cost?

@yangyeum If Itunes does not see it, it will not power on or reset, you don't see an image (even with a flashlight), it sounds like something more serious is going on than just a backlight.

If you were "Practicing", I'm assuming you don't have much experience and may have made a simple mistake by not getting a connector seated correctly or may have knocked off or damaged a small component near a connector.

First, open the phone again. Make sure you disconnect the battery flex (But be gentle around connectors only lifting them away from board without scraping or hitting the board itself).

Disconnect the flex cables to the screen.

Now, a couple things...

Did you keep track of the screws you removed from the shield protecting the connectors from the LCD? It is EXTREMELY important that you replaced the screws back in the same hole they came from. If you did, then great...if not, then I think I know what your problem is.

If you put the wrong screw back in the wrong hole, you can cause what is called "Long Screw" damage to the Logic board.

Each screw is a different length, and if you attempt to put a longer screw in a shorter hole, it will "Bottom out" against the logic board where microscopic traces are located connecting different circuits within the board. If you continue to tighten the screws, they will embed themselves and sever the traces, requiring a very difficult microsoldering trace repair on them to reconnect them with micro jumpers.

If this is the case, it is a specialized service that only a handful of experienced Microsoldering techs can perform. I would suggest looking for a local shop (if available) to inspect your board with a microscope to determine just how bad the damage is (Most do not charge if no repair is done). If not available in your area, look through the Pros listed here on IFIXIT and you could get an estimate and mail in service.

If that is not the case, then look closely with magnification at the connectors and surrounding areas for inadvertent damage you may have caused...see if there is any obvious signs of components lifted, damaged or missing.

If so, this is an easier repair and would not cost as much...follow the same instruction on finding a reputable repair tech to inspect and quote.

Repairs can cost anywhere from $50 up to $300 depending on what is wrong and very difficult to give a quote without inspecting the board first. Again, most reputable places will not charge for the inspection with no repair...

If you are sure its not long screw damage and there is no visable damage, try to carefully reseat the connectors...Battery last and plug it into a cable with itunes running and see if it sees it again or if a light can see the screen.

Best of luck!