if it's anything like the iPhone my parents have, then when their SIM locked them out, they had to go on the AT&T website to find the exact code.
If it's a SIM code that you set, then I would try a factory reset, since at this point you don't really have anything to lose.
Otherwise you can call MetroPCS and have them troubleshoot it, but please note that rooting and loading a ROM on it most likely voids your warranty, and they may refuse to help you, since they can say it was a "user error."
Hope this helps, and best of luck to you all! =)