Hey I have always had this problem and I really can't get an explanation of why or how to fix this. I have frontier DSL and sometimes certain websites will just stop working for me for a week or two, but i can get to these sites using a proxy. I am the only one in the house with access to the router and the modems settings (mainly because my parents dont know how to work them) so its not like im being blocked by someone. So can someone help me out and try to give me a reason why this is happening, or how to fix this?
How about when you type in the site's IP address instead of web address?
I'm thinking it might be a DNS problem on the ISP's side. You can try manually set DNS to the one provided by OpenDNS for testing if that's the case.