@salimjuma this 'lights up then goes dark.....when connected to the charger" means your phone recognizes that a charger is connected. For now, you want to start with replacing the battery first. Then re-evaluate.
Something like [Nokia 5 |this video] should help you out.
Let us know what happens when you have a new battery installed.
While you replace your battery, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.