All ports appear blocked

Recently tried Charter as the only other ISP in my area sucks absolute balls.  However, uTorrent doesn't work, and port checker tests reveal that nobody can access ANY ports on my computer.  Three different websites, checks on common ports and random ports.  EVERY port is apparently blocked.  I called Charter about this but half of them say Charter doesn't block anything, and the other half don't know what ports are.  I only have Windows Firewall and for the tests even that was disabled.  I didn't connect it to a router, my computer has a straight connection to the modem.  I even tried it with another computer of mine.  (one's Vista, one's XP).
Any suggestions?  Internet with AT&T cuts out three times a day, and Charter's the only one I got left.

>>4
there was no router, as I said.  Also on Vista I reset the TCPIP stack, and on the XP computer as I also said it was a fresh install.  I also switched network cables a couple of times.  The only thing that I didn't replace was modems.  Not to mention, that if I plugged in the cable going to the AT&T modem into the same jack on my Vista or XP computer, everything worked as expected.