it's very possible the ISP changed something. Like maybe they were issuing ips for every request, instead of only 1 per modem. who knows for sure? You can call the ISP and ask if something changed. I'm sure they will tell you.
Totally agree with purchasing a stand-alone router rather than depending on your PC providing protection for your network. I know it kinda sucks buying hardware for something that used to work but take it as a blessing in disguise...
