Im sorry please try a new phone, the D500 has been discontinued quite some time ago and the cost of the handset its just not feasible to justify a new battery and charger or attempting repairs...
If you do wish to attempt repairs, it could be a number of things, the charger could be faulty even if it does light up... The battery could be faulty and wont allow it to charge, the connector at the bottom of the phone could be damaged, check the bottom of the phone the connector pins where the charger makes contact.
MobilePhoneFX.com, June 2008
