A rebooting of your internet hardware (whatever form it is) isn't a bad place to start either.
nslookup via command prompt a website giving you trouble and use one of the resulting IPv4 addresses instead, and if ALL of them work perfectly fine, Domain Name System IS definitely messed up and contact your ISP, there are free DNS servers out there if you dare too, for testing.
nslookup <sitename using alphabetical characters here>
Example:
nslookup google.com ........gave me about 10 IP addresses to use instead. 74.125.224.230 was one, and verified works, it could be dynamic though, that is why we use DNS in the first place, so the IP can be changed, but the NAMED version gets pointed to the right IP via the DNS servers and the result was the wars over names and .com .net whatever, funny to me that .extensions have to get "approved".
If I really want ihate.you to point to a certain site, I can manage it!!!

[hint HOST file]
Use
ipconfig /all from command prompt for all the Internet settings info you are using, includes DNS, mine points to my router which is handling it via my Internet Service Provider's DNS settings.
[expect 192.168.x.x as likely result if yours is using a router for DNS as well]