Screen lit dim after the start up

I presume you changed the screen because it was cracked or broken. Was everything working fine before you replaced the screen?

I would go back through this guide, step by step to insure you did everything correctly. Make sure you disconnect the battery before removing the screen. You may have either a defective replacement screen or the connectors were not seated properly.

When you open the phone, keep track of the screws, especially these five. You'll note that the bottom two screws (yellow & orange) only have 0.1mm difference in length. If you put them in the wrong place, you can cause what's known as Long-Screw Damage. Typical symptoms f LSD are blue screen (blue screen of death or BSOD) or infinite boot looping.

Your description almost matches that so hopefully that is not your problem. Go through the guide and come back and comment on this or other answers to let us know what you find. Then we can guide you on the next step.