First where did you purchase the CPU from, Ebay or did you buy it from a friend or given as gift?
Anyway, You would need to contact AMD Support and give them your AMD CPU Serial number to see if it is a valid AMD CPU and if it is still under Warranty. If you got it from another User need to find out if the Warranty is also extended to the second buyer as being Used.
Here AMD Support website shows you how to know if your AMD CPU is a valid AMD CPU or not: How to Determine the Authenticity of an AMD Boxed Processor?
Here you can verify your AMD CPU Serial Number: AMD SMS Serial Number Verification System
Here is AMD Warranty Services to find out the Warranty and conditions for your CPU: Warranty Services | AMD