27-09-2011 12:05 - edited 27-09-2011 12:07
Most likely, you don't have a PIN for Nokia's music service.
Only special models sold separately as "Comes With Music" (CWM) or "Ovi Music Unlimited" (OMU) include such a PIN code. If you bought a "regular" phone without CWM/OMU, then you're not eligibile for the free, unlimited music.
Also worth noting, that all phone models have never included CWM/OMU, and when they have, they have been for sale both with CWM/OMU (higher price) and without (lower price). I don't know if the C3-00 was ever sold as a CWM/OMU version anywhere (availability has also varied by country).
Otherwise, you need to buy music credits using a credit/debit card first from the Nokia Music Store, or some other online music store (such as iTunes), or rip your own CDs.
If you bought an actual CWM/OMU model, then the sales package (box that the phone came in) will say so, and the PIN should be inside on a separate flyer/certificate.
If you have a genuine CWM/OMU model, but the PIN/flyer/certificate is missing, then call Nokia's Customer Care (see the "Contact Us" link on this page) and ask them for help.
Note that if you bought a second-hand (used) CWM/OMU model, and the original owner already registered the service for himself/herself, you're probably out of luck (Nokia probably won't "transfer" the registration to a second/new owner).