Try disconnecting the battery even if you let it die completely there is still enough energy to maintain the cache to completely drain the mem you need to disconnect the battery and then hold the power button down for 60 seconds or so . This guide will help with disassembly.
[guide|62600]
If after rebooting you still have no joy it may be that you will need to replace the screen assembly as the LCD may have died. Maybe while you have it open check the screen is properly plugged in . Hope this helps