Web server suddenly stopped working

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http://serverfault.com – I have a web server, which was working fine. It also was an FTP server and a Windows Remote Desktop server, all working fine. Someone called our ISP to increase the internet speed, and suddenly nothing works - I can connect with Teamviewer, but HTTP, FTP & RD doesn't work. Disabled firewall. Ran Wireshark - the packets don't come through at all. Set the webserver to port 20111, in case the ISP is blocking port 80, and again, the packets didn't come through at all. (localhost:20111 works fine) Port forwarding is set up for ports 80, 21, 3389 & 20111 to (which is the correct (HowTos)