There are several reasons, like bad battery, bad charging connector, bad charger, charging pin problem, charging ic, etc..
You need to try with another charger and with another battery. If changing the charger and battery don't help, follow the instructions below;
First, remove the battery, clean the contact points on the battery and also clean the battery interfaces on the mobile. You also need to check the charging connector and clean whatever is possible. Use soft brush or cotton with Ipa solution or alcohol/spirit/acetone to clean all the metal contacts. Try charging again.
If the above method don't help, you need to change the charging pin;
Still the problem persists, then check the charging ic. Perhaps jumpering will be necessary.
If you are not sure what you gonna do with ic, I don't recommend to play around with it, rather take it to a mobile repairing shop or nokia service center and get it fixed. You may damage another components.
I wish you good luck.
Thanks for using FixYa.