Calico Jack

Booted up the computer this morning to find I cannot access anything online.
Browsers won't load anything, email won't connect, antivirus etc can't connect to access updates etc etc etc.
I have a D-Link modem/router and it tells me I'm connected at my usual speed.
Rang tech support, they say all is fine on their end, line is good, connection is good and they can see no problems.
Got our tech guy to come and look...he can see no reason why things won't work either.
Powered off the modem/router, checked all cabling including the phone line...everything plugged in.
We've got 3 p.c's all networked yet none can access anything online.
Done a full virus scan, adaware and windows defender scans...all clear.
Disabled firewalls...nothing connects.
I'm using my kids dialup account to post this.
Anyone got any ideas? Think my modem/router is fucked?