Display is black though the screen is responsive

My iphone got wet in rain. I had given in some some shop, he said the Dock Connector was having issue(since he was not able to restore), so he replaced that, but could not make the phone working.

Now the phone works perfectly like it rings if anyone calls, I can switch on/off the phone by swiping on screen, it vibrates also.

I just see the apple icon for few microseconds when the phone boots, then the screen is completely blank. As my phone is not under warrenty and moreover the guy changed the Dock conenctor, the Apple guys saying they will not touch the phone since it is tampered outside Apple.

Any help please how to make the screen working?