First things first, to rule out redirecting malware, if you have any other internet capable device, change it to the same DNS provider and see if you get the same results.
If you don't, you probably have malware on your pc. If you do get the same results, it is either the DNS provider or your ISP.
I have no experience with Google Public DNS as I haven't had time to mess around with it, but if you set your dns server to Opendns just for a moment and see if you get redirected to their service or that address you posted originally.
If with OpenDNS you still get redirected to your one it is likely that your ISP is redirecting people.
If you go to the OpenDNS failure page, it is probably the current DNS provider that was forwarding you to there.
And to answer your question...
The above is how to test if it is your ISP, Malware or your DNS provider.
As for what to do, if it is your DNS provider - Switch, if it is Malware - Fix/remove it, if it is your ISP - switch!