My phone 6120classic doesn't support MP4 file.why?

SOURCE: my phone 6120classic is formated

I just had the same problem. Performed the green key, * and 3 button. Still came up with the enter lock code screen. Just enter the default 12345 and should be fine, then go into phone settings and turn off the lock code on change of sim card. Hope that helps. Keep in mind it will wipe your phone clean back to default. The lesson here is don't forget what you change your code to, I have learned my lesson.