Help me, please!! Problemns with new macbook pro

Hi
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I just bought my new mackbook pro online and it came with Mac OS X Lion operating system.
When i took the computer, everything was fine. But i couldnt access my user folder on Finder and i tried to fix this issue. I ended up doing something really wrong because now i turn on my computer and my login and/or passwords are incorrect and i can not log on my laptop.
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I searched for answers on diferent forums and i tried to reboot the system in order to reset the password, but nothing worked. Also i tried to install Snow Leopard (restarting, holding C and selecting the installation dvd), but then it appead a box telling me to restart the computer (and this happens everytime i try to install snow leopard).
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I'm worried because i bought this mac on apple online store while i was on the US (and i am from Brazil) and i dont have any support in my country.
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Please, help meeeeee! What do i do???

If your MBP came preinstalled with Lion, you can not install Snow Leopard. You would need a Snow Leopard DVD made specifically for your machine. The latest Snow Leopard specific DVD for the MBP and iMac was 10.6.6.

You're going to have to contact Apple and buy the thumb drive from them which has Lion 10.7.1 on it if you want to reinstall clean.

Have you tried booting your machine and holding down the Option key? You should be able to do that and select the Recovery partition in order to reinstall Lion. However, since you're in Brazil I don't know how you're going to be able to download anything direct from Apple.