Why does my Nokia 6300 ask for security code on startup?

[Draton22]

I didn't put a security code on the phone but it asks for it. Now it won't open.
It's just a backup phone not my main phone but I want it to become usable.

 

[NancyBee]

because 'lock if sim changed' must have been activated. U dont remember doing that? The default code is 12345 unless u changed it. If u did and dont remember it, take ur phone to nokia care with ur i.d and purchase/contract papers to prove its ur phone, and they will unlock it and reset the lock code for u. Its the only way.