Does the screen permanently stay dark now?
Does the charging LED still work when plugged in? (I.e. Do you get a yellow or green light when plugging in and charging the battery?)
I am wondering if it is just the screen that stays dark, or if the phone is shut down and doesn’t boot (the latter could be a problem with the battery, which may need to be reset).
If disassembling the display and cleaning contacts didn’t get the screen working, but you think the phone itself does work/boot, then I would try to get a replacement screen (as I think the screen is malfunctioning in this case).