Routers supporting Vista

I have been using Vista for nearly 3 years connected with Cisco 575 LRE (hard wire). I was able to access all internet pages without any problem.
Then, approx 6 weeks ago things changed. I couldn't access my Hotmail account, my online banking accounts, I can't even check flights with Ryanair, and lots of other websites. I thought at first it was secure sites only that I couldn't access, but its not. I contacted my internet provider who has checked the network, and told me the network is working OK. I had Windows Vista reinstalled, but that hasn't worked either.
If I take my pc to another service provider, it works! It also works with a mobile 'dongle'. I am now at a loss as to what to do.
Can anyone suggest anything I haven't tried. Or should I change my router?
Cheers
Vic