This could be a wide range of things from a defective LCD stated to your connector plates on the logic board they are very fragile and if bent will not work properly. My suggestion is if you did this yourself is look at your quality of replacement and that might be your solution and make sure you ordered the right model number a 6 digitizer might not work with a 6s phone and vice versa
Could be as simple as a cable came loose, to you need a new screen, google the teardown for your phone and follow the best one you can find (of course you dont need to take your phone all the way apart just follow the screen assembly tear down the reconnect the cables)
You couldve also damaged your logic board as well in that case you will need a new logic board. easy way to tell is to look at the connectors on the last one on the left, that is the connector for the screen and if there is any damage to the connector you will need to replace the logic board.
Do it yourself if you feel comfortable, look into youtube videos internet etc research the crap out of it, It could also just be your processor or something got knocked loose when you dropped the phone.