there can be couple different problems:
1) LCD you installed was defective (or damaged during installation, trust me that's common for DIY)
2) LCD is not plugged in correctly to the board ( you can try to open it and re-attach the LCD connector to the board and restart the phone holding home+power button)
You can also check, if you still have the old LCD assembly, you can connect it from outside bu just disconnecting cables for LCD installed on the phone at this time and bend them back so you can give enough space for different LCD to be connected just plug it until you hear/feel the click and try to power on the phone. In case this will work you might need to replace the LCD screen assembly .
3) LCD connector on the board is broken (see if this was not damaged during installation)
4) Yay! any water damage???