can't get Yahoo and a few more sites

I am using Win 98 and dial up service Netzero.
I don't know where the problem lies, either with my
computer or netzero? I don't understand how I can get on-
line and be able to see certain sites but not others. I
have no trouble going to hotmail, but am unable to go to
Yahoo. This has been happening for awhile, lasts about a
week then no trouble for a few months and then alas, it
happens again.
I turn the computer off and unplug and retry but no luck.
Please help, do you think its the servers at netzero?