replaced screen now having issues :( galaxy s4 i9505
Your display issue is almost certainly a bad connection on one of the ribbon cables that connect the display to the circuit board.  One of the two cables you had to disconnect didn't get fully seated in the connector, leaving some traces intermittent.  Assuming the connector wasn't damaged when you disconnected the old screen, you may be able to restore correct operation by disassembling to the point where you disconnected the screen and digitizer cables, then carefully following instructions to reconnect those ribbons, followed by completing the reassembly.

You should also be able to install the battery and power up the phone to check things before fully reassembling, which will save time if you have to take several tries to get a good connection.