first of all.. you will have to un-install / remove the cap (crown) .. Get a Root canal done from a specialist (if the tooth is painful) .. after the procedure is completed, you may re-install/re-fix the cap again.. provided no changes in the tooth anatomy has been done during the treatment ..
if the cap doesnt fit.. you may have to make a new cap/crown for your tooth ..
Next Steps
Warranty .. shall depend upon your dentist ..
Health Tips
get your self examined by a dental specialist.. after taking appropriate xray / rvg and clinical examination, he would advise you the best possible treatment .. :-)