Worked fine but then black screen after waking from sleep

I replaced the screen and on starting up everything worked fine, both the lcd and digitizer. After putting it to sleep, however, it has a black screen. If I disassemble again, undo and redo cable connections, same thing happens. Works fine until you hit the sleep button and then it has a black screen. I put the original/cracked screen back on and everything worked. Used it that way for a couple weeks. Put the replacement screen on again and have the same problem—works until it is put to sleep, then black screen. Any suggestions are appreciated.