I powered with 3.3volts because today i learned that serial working only under this voltage.
That proves that you should not trust everything you read, it is nonsens.
I don't know the core you are using, as I said in previous post I am using this one:
is there any problem that windows isn't in english language? I think i have tryied everything...
No mine windows is danish, and that dosn't give me any trouble.
Are you using SoftWareSerial for communication ?