Nop, no firewall. The cablemodem has not been tested with other computers, but it is the one that the ISP "rent" to my friend (here, in mexico, this is very commun, you have not to buy the modem), so,, it sholud work fine...
Anyway, the internet connection works for a few minutes, and it is very fast, but after a while, it just sopt working.... so, the modem actually works....
I will try all the scan that fed recommend, to see if a can find something strange....
Thanks