Lines on display after reconnecting it

Either you've damaged the display connector or cable, or it just isn't plugged in correctly.

Start out by unplugging the display and check the connectors, both on the cable and the logic board. Make sure there aren't any bent or broken pins and examine the cable for tears or excessive bends. If it all looks good, clean the connectors with 90% or higher concentration isopropyl alcohol, let them dry then plug them in, making sure they're fully and firmly seated.

Retest and see if it's working now. If not, you'd best test with another screen if available, but if not then the next suggestion would be to replace the screen and hope that does the trick. Given the age of the phone parts are getting dirt cheap so I'd be surprised if you had to pay more than about $15-20 USD for a replacement screen.